15 Top Legacy Software Modernization Companies in Europe for 2027: Comprehensive Overview

88% of the euro area’s significant banks depended on at least one end-of-life system for business-critical work.

The same pattern runs through manufacturing, construction, logistics, healthcare, insurance, and more, where core systems still work but grow harder to change. For your business, the hard part is replacing that code while orders and payments keep moving through it. The partner you choose decides whether that move runs in safe phases or turns into a costly outage.

This article covers 15 top legacy software modernization companies in Europe, with the latest European statistics, a 5-phase roadmap from audit to go-live, and practical tips for picking a partner for your business.

Key Takeaways

• Europe’s application modernization services market stands at $7.56 billion in 2026, and Market Data Forecast projects $25.60 billion by 2034.
• Cloud use keeps rising, with 52.74% of EU enterprises using paid cloud services in 2025, mostly for e-mail, office software, and file storage.
• Banks carry a heavy legacy load: 88% of the euro area’s significant banks depended on at least one end-of-life system for business-critical work in 2022.
• Tech debt can equal 20% to 40% of a technology estate’s value, according to a 2020 McKinsey survey of 50 CIOs.
• Every firm in the list keeps engineering teams in Europe, publishes legacy projects with named clients or measurable results, and has a verifiable track record.
• A low-risk roadmap runs in 5 phases: discovery, target architecture, pilot migration, phased rollout with parallel running, and post-launch optimization.
• Before you sign, run a short paid assessment, ask for case studies on your stack, and meet the engineers who will do the work.
• AI tools now speed up code analysis, documentation, and testing, while architecture and cutover decisions still need experienced engineers.
• The list of top legacy software modernization companies in Europe for 2027 includes Reenbit, Capgemini, adesso, Zühlke, Netcompany, Kainos, Accedia, Scalefocus, iteratec, Equal Experts, Codurance, Exxeta, ELCA, Siili Solutions, Evozon.

European Legacy Modernization Statistics for 2027

Spending on modernization services keeps climbing across Europe, while banks, insurers, and mid-size enterprises still run billing, claims, and ERP workloads on aging platforms. These statistics help you size the gap and set realistic expectations with your board:

• Market Data Forecast puts Europe’s application modernization services market at $7.56 billion in 2026 and projects $25.60 billion by 2034, a 16.47% compound annual growth rate for services spend across the region.
• Eurostat found that 52.74% of EU enterprises used paid cloud services in 2025, up 7.42 points from 2023, across firms with 10 or more employees, mostly for e-mail, office software, and file storage.
• Bitkom surveyed 603 German companies with 20 or more employees in 2026 and found that 86% use cloud services, with 47% of IT applications already in the cloud and firms expecting 58% within 5 years.
• AI use reached 19.95% of EU enterprises in 2025, Eurostat reports, up 6.47 points on 2024 in a survey that covers firms with 10 or more employees across the 27 member states.
• The UK National Audit Office counted at least 228 legacy IT systems in government departments as of March 2024, and departments lacked fully funded remediation plans for 53% of them, or 120 systems.
• McKinsey’s 2020 survey of 50 CIOs at financial-services and technology firms with revenue over $1 billion put tech debt at 20% to 40% of the value of their technology estate.

How We Build the List of Top Legacy Software Modernization Companies in Europe

Choosing a modernization vendor for your business depends on several factors. We selected every firm in the list against the same 4 factors, and you can use them to assess any other vendor you consider. Let’s look at each one.

European Roots and Delivery

Each company keeps headquarters and engineering teams in Europe, so your project gets overlapping working hours and engineers who work with EU data rules on every engagement. That filter matters when your data falls under GDPR or your sector answers to DORA or NIS2, because the delivery team needs to work inside those rules from the first sprint.

Dedicated Modernization Practice

Modernization has to appear as a service on each firm’s own site, backed by at least one published legacy project. You can judge depth faster when a firm shows how they handle work like this:

• Refactoring or re-engineering code that your teams still need to extend
• Re-architecting monoliths into services, containers, and APIs
• Migrating databases and workloads to cloud platforms
• Replacing mainframe or end-of-life platforms with supported stacks
• Running releases through automated pipelines after go-live

Published Results and Named Cases

Claims count only when they come with evidence a buyer can check, such as a named client, a measurable outcome, or a dated case study. That rule ties the list to delivered work and gives you a fast way to see whether a firm has solved a problem close to yours. Figures in each profile come from the firm’s own pages, filings, or press releases, so you can check every number.

Verified Reputation and Independence

Each firm also needed a public track record and an ownership status you can confirm today. Here is what counted:

• A verified Clutch rating with client reviews, or a public listing with audited annual reports
• Named case studies for firms without a Clutch rating or a stock listing
• Independent ownership, with no acquisition by or merger into another group
• Company sizes that range from global integrators to mid-size consultancies, so your shortlist fits your budget and scale

15 Top Legacy Software Modernization Companies in Europe in 2027

Every firm in the list keeps engineering teams in Europe, publishes legacy modernization projects with named clients or measurable results, and has a verifiable track record. Here is a quick overview before the full profiles:

Reenbit

• Founded: 2018
• Legacy Expertise: Legacy .NET systems, Dynamics NAV ERP, on-premises servers, mainframe workloads
• Primary Tech Stack: .NET, Azure, Angular, React, Blazor, Kubernetes
• Engagement Model: Dedicated team, tech partnership, IT staff augmentation

Reenbit is a top legacy software modernization company in Europe for growing companies that cannot pause operations to rebuild. Backed by Microsoft Partner status, their team of 100+ engineers has delivered 75+ projects over 8+ years. 88%+ of their specialists are Microsoft- or Azure-certified, as well as ISO 27001:2022 certified and GDPR-compliant, and deliver Azure support for clients in healthcare, fintech, manufacturing, construction, energy, and more.

Every engagement starts with a 1- to 2-week Assessment Sprint that maps the legacy system, constraints, and technical debt, then ends in a roadmap and a decision to rebuild, re-architect, or refactor. From there, delivery runs in phases, so systems stay live during migration.

Across 23 Clutch reviews, clients cite transparent communication and predictable delivery, and an ERP modernization for a cleaning services company reached 99.7% crash-free sessions.

Delivery highlights

• An autonomous AI engineering agent delivered legacy modernization 30x faster for an energy platform and cut key operations time from 30–40 seconds to 3–6 seconds.
• Brands of Scandinavia saved €400,000 in the first year after a back-office sync across 5+ production and commerce tools.
• Cloudbooking’s space management platform runs on Azure, Kubernetes, .NET Core, and React, with 27% lower maintenance effort and a 99.9% sync rate.
• Database migrations target Azure SQL, Cosmos DB, and MongoDB.
• Cloud migration work uses Azure Migrate, Site Recovery, and Database Migration Service.
• DevOps and CI/CD pipelines automate releases, with post-launch support after go-live.

Capgemini

• Founded: 1967
• Legacy Expertise: COBOL, PL/I, Natural, CICS, and DB2 mainframes
• Primary Tech Stack: AWS, Azure, Google Cloud, microservices, serverless
• Engagement Model: Managed services, POD-based delivery teams

Capgemini launched a gen AI and agentic AI offering for COBOL mainframe refactoring in May 2025, built on the CAP360 and SmartSDLC suites. Published gains reach 30% to 50% faster transformation and testing and 10% to 20% improvements in early discovery and planning. Forrester named the group a Leader in The Forrester Wave for application modernization and multicloud managed services, Q1 2025.

Targets cover AWS, Google Cloud, and Microsoft, with microservices, containers, APIs, and serverless as the standard architecture. For one investment firm, the practice moved a mainframe with 40+ million lines of code and 5,000+ DB2 tables onto AWS.

Delivery highlights

• Group revenue reached €22.5 billion in 2025 across 423,400 employees.
• Over 57,000 custom business software engineers work across the group.
• Named application clients include Penske, EDF, Anglian Water, BMW, and VINCI Energies.
• The Assess, Transform, Cloud RunOps method structures each mainframe program.
• AWS Transform for mainframe and Amazon Bedrock AgentCore feature in the composable modernization approach.
• 44,000+ trained DevOps professionals support release automation.

adesso

• Founded: 1997
• Legacy Expertise: COBOL and PL/I mainframes, IBM Db2 for z/OS, IMS DB, JEE applications
• Primary Tech Stack: Java, Spring, Spring Batch, Angular, AWS, Azure, Google Cloud
• Engagement Model: Managed services, SmartShore nearshore delivery

adesso converts COBOL and PL/I code to Java with adesso transformer, a 7-tool suite for code, UI, analysis, batch, conversion, editing, and testing, with an option for 100% automated transformation. Mainframe exits sit at the center of that work: DAK-Gesundheit saves a double-digit million euro amount per year since the health insurer switched off the IBM mainframe.

Under a 3-year framework agreement, Provinzial chose the group to migrate COBOL programs into Java systems. Beyond code, MIGSuite handles data migration with IDW PS 880 auditor certification, and the cloud practice counts 240+ AWS certifications and 1,000+ Microsoft experts.

Delivery highlights

• Revenue reached €1.47 billion in 2025 with 11,298 full-time equivalents.
• SmartShore delivery runs through initiation, SmartStart, implementation, and handover phases.
• TEAG moved SAP S/4HANA Utilities to the cloud in a 4-year project with an 8-digit contract value.
• Application management draws on 800+ specialists with on-call support up to 24/7.
• ISO 27001, ISO 9001, and ISO 14001 certifications cover the managed services line.
• Code transformation, UI modernisation, data migration, and testing make up the modernization offer.

Zühlke

• Founded: 1968
• Legacy Expertise: Mainframes, monolithic applications, COBOL, C, and Assembly codebases
• Primary Tech Stack: AWS, Azure, Mendix, Google Cloud
• Engagement Model: Managed services, scalable engineering teams

Zühlke applies Cybernetic Delivery, a method that embeds tools such as GitHub Copilot, Story-GPT, and Review Bot into legacy work, with about 30% efficiency gains on a platform holding millions of lines of undocumented code. Alongside that, a digital twin approach builds a knowledge base through reverse documentation, which a private bank used to machine-read core systems in natural language.

Swisscom split a monolithic customer application into mobile, billing, and email modules with the consultancy. For N Brown, the team moved an account portal off mainframe dependency onto AWS microservices. Certifications span ISO 27001, ISO 9001, and ISO 13485.

Delivery highlights

• 17 offices across 10 countries host the engineering teams.
• UNIQA’s AI chatbot delivered a 95% efficiency increase.
• Julius Baer’s GenAI infrastructure went live in 8 weeks.
• Wincasa’s legacy application now runs on Azure.
• Managed services include application management, platform operations, and managed cyber defence.
• AI-augmented security operations respond to alerts in under 3 minutes.

Netcompany

• Founded: 2000
• Legacy Expertise: Mainframes, COBOL, legacy Java, monoliths
• Primary Tech Stack: AMPLIO, Azure, AWS, Dynamics 365, Salesforce, SAP BTP
• Engagement Model: Application maintenance and operations under multi-year framework agreements

Netcompany modernizes core systems with in-house platforms such as AMPLIO and AMI, plus Feniks, an AI tool for learning and redesigning legacy code. For energy and telco group Norlys, the team moved 98% of 450,000 customers off 3 legacy systems.

Banking work runs through Netcompany Banking Services, a legacy-free core platform with open APIs for 50+ financial institutions and 2+ million end users. Certifications cover ISO 27001, ISO 9000, and Cyber Essentials Plus, with SAP Partner status for EMEA.

Delivery highlights

• 9,500+ professionals work across 10+ countries.
• A COBOL mainframe replacement on AMPLIO cut maintenance costs by 30% for a system with €30 billion in annual payouts.
• The financial services practice counts 1,000+ specialists.
• Norlys received a Field Service Management solution in 3 months.
• Operations reach a 95% virtualization rate.
• Cloud partnerships include Microsoft, AWS, Oracle, and Google.

Kainos

• Founded: 1986
• Legacy Expertise: Mainframes, Perl services, on-premises ETL, end-of-life data centres
• Primary Tech Stack: AWS, Azure, Google Cloud, Node.js, Java, .NET
• Engagement Model: Phased design, delivery, and run; managed services with dedicated teams

Kainos moved a multinational insurer’s on-premises ETL onto an event-driven AWS architecture, cutting job runtime from hours to minutes for a roughly 900% speed increase. Transformco, owner of Sears and Kmart, left a 40+ year-old mainframe for Workday Adaptive Planning in under 5 months and retired 30 years of reports.

As an AWS Premier Consulting Partner with 500+ certified engineers, the consultancy holds Migration, DevOps, and SaaS competencies. Across 100+ cloud projects, the practice reports a 50%+ average cost reduction and 12 weeks on average from design to go-live.

Delivery highlights

• FY26 revenue reached £431.1 million across 1,253 customers.
• Managed services cover 340 clients with 1,500 engineers under ISO 20000 and ISO 27001.
• Financial services clients include Generali, FBD Insurance, Sun Life Financial, Global Payments, and Stripe.
• 24/7 L2 and L3 AWS support runs for a sanctions-screening platform that major banks rely on.
• Partner status spans AWS, Microsoft Solutions Partner, and Google Cloud.
• 3,132 people work across 18 countries.

Accedia

• Founded: 2012
• Legacy Expertise: PHP and Laravel, AngularJS, MySQL 5.7, legacy core banking, desktop XBRL apps
• Primary Tech Stack: .NET, ASP.NET Core, React, Next.js, Node.js, Azure, AWS
• Engagement Model: Dedicated teams, project-based delivery, staff augmentation, advisory

Accedia modernizes banking platforms while old and new systems run in parallel, a method that moved a bank from MySQL 5.7 to 8.0 across the whole platform in about 2 months. For Castle Trust Bank, a 10-year partnership on the OmniPort lending platform now supports 200,000+ lending decisions a year, with about 80% of customers getting an automated decision within minutes.

Their engineering capacity stands at 250+ engineers, with AWS Consulting Partner status since 2018. In one financial-services rebuild, a data storage redesign made the application more than 10 times faster.

Delivery highlights

• Banking clients include Shawbrook Bank, Société Générale, and Alexforbes.
• The AF Connect platform serves 100,000 monthly users.
• MRI Online moved from PHP and WordPress to React, Next.js, and NestJS for 700+ hours of courses.
• Certifications span ISO 9001, ISO 14001, ISO 27001, and TISAX.
• 91% client retention spans 150+ clients in 20+ countries.
• An equipment-finance company replaced a paper-based credit process with .NET, SQL Server, and Azure.

Scalefocus

• Founded: 2012
• Legacy Expertise: IBM integration stack, C++ monoliths, PHP and Oracle back ends, legacy mobile apps
• Primary Tech Stack: Java, Spring Boot, Scala, React, Kubernetes, .NET
• Engagement Model: Project-based dedicated teams, staff augmentation, one-team adoption

Scalefocus upgrades middleware and monoliths for operators in aviation, gaming, and energy, including IBM IIB, ACE, MQ, DataPower, and ODM components that neared end of support at an airline. For a gaming operator, the team rebuilt a C++ monolith on Java, Spring Boot, Scala, and Kubernetes and reached 99.9% availability outside maintenance windows.

Delivery runs through project-based dedicated teams, staff augmentation, and nearshore delivery centers, and 80% of engagements involve managed teams or end-to-end product work. That work covers 90 business-critical systems with PHP and Oracle debt at a utility networks provider, where 600 forms moved to digital.

Delivery highlights

• Paysafe works with 4 dedicated development teams under a 10-year partnership.
• Certifications include ISO 9001, ISO 27001, ISO 20000-1, and ISO 14001.
• Partnerships span AWS Advanced Consulting Partner, Microsoft Solutions Partner, Databricks, and MuleSoft.
• 1,000+ projects and 300+ clients make up the delivery record.
• A national lottery’s rebuilt mobile app rose from a 3.7 to a 4.9 store rating and serves 600,000 monthly users.
• The AION platform deploys AI on sovereign infrastructure.

iteratec

• Founded: 1996
• Legacy Expertise: Decades-old core systems, a 40-year-old reservation system, legacy sales platforms
• Primary Tech Stack: Cloud-native, event-driven microservices, AWS, sovereign cloud
• Engagement Model: Fixed-length entry packages, then phased transition

iteratec replaced the 40-year-old reservation system of Deutsche Bahn with the RiFF platform, finishing 10% under budget and 6 months ahead of schedule, with 5x lower operating costs after modernisation. During rollout, the new system went from 1 to 100+ trains a day with zero outages and peaks of 5,000 requests per second under 50 ms.

Legacy Intelligence structures the work in 4 phases, from inventory and assessment through strategic and tactical design to a transition with parallel operation. DACHSER removed 70 redundant process attributes through that approach without interrupting operations. Employees own the business through the nurdemteam eG cooperative.

Delivery highlights

• Entry options include a 4-day Legacy hyperSPRINT, a System Health Check, and a 20-day System Review.
• Revenue reached €62.5 million in 2025.
• 1,000+ completed projects span 350+ customers over 30 years.
• ISO 27001:2022 and TISAX Level 3 certifications cover the delivery organization.
• DB Komfort Check-in moved off the legacy sales core onto the Vendo platform on AWS in 2024.
• Ragn-Sells cut physical testing costs by 70% and reached market 10x faster.

Equal Experts

• Founded: 2007
• Legacy Expertise: Monoliths, on-premises data centres, a 15-million-line .NET monolith
• Primary Tech Stack: GCP, Snowflake, Kubernetes, microservices, event-driven architecture
• Engagement Model: Small senior teams that build in-house capability

Equal Experts modernises legacy systems by improving, replacing, replatforming, or re-architecting components one at a time while the business keeps running. At John Lewis, deployments rose from 10 a year in 2016 to 4,000 a year in 2019, with time to customer down to 90 days from 6+ months.

For an insurer, a white-labelled engine reached £600,000 in daily revenue and 900+ policy sales per day by September 2025, with bug-fix deployments down to 10 minutes. Ownership sits with a trust that the 4,070-member network holds collectively.

Delivery highlights

• 90% of network members bring 10+ years of experience.
• A retailer decoupled order management from a monolith with a new event-driven system in 12 months.
• John Lewis runs 90+ self-serve data products and 150+ pipelines on Snowflake and GCP.
• Partnerships include AWS and Google Cloud.
• 200+ companies have worked with the network.
• Modernisation services cover legacy migration, architecture modernisation, platform engineering, cloud optimisation, and security.

Codurance

• Founded: 2013
• Legacy Expertise: Monoliths, VB6 applications, a 20-year-old EHR codebase, on-premises trading platforms
• Primary Tech Stack: C# and .NET, AWS, Azure, Google Cloud, OpenTelemetry
• Engagement Model: 2-week AI and Engineering Assessment, embedded AI champions, agentic AI design and delivery

Codurance decomposes monoliths with the Strangler Fig pattern and Domain-Driven Design, backed by characterisation and mutation testing, and modernises platforms incrementally without a rewrite. Using AI-assisted conversion, a VB6 to C# .NET migration finished 50% faster than an 18+ month rebuild estimate.

Engagements open with a 2-week AI and Engineering Assessment and aim for measurable results in 6 to 12 months. In financial services, concurrent incidents on a monolith fell from 90 to 0 within 12 months. Certifications include ISO 27001 and Cyber Essentials, and partnerships cover AWS, Microsoft, OpenAI, and the Anthropic Claude Partner Network.

Delivery highlights

• eClinicalWorks cut a QA cycle from 2 weeks to under 2 hours and trained 100+ developers.
• ASOS re-architected and moved to the cloud with craftsmanship coaching for 40+ development teams.
• M&G moved from a legacy trading platform to Aladdin on Azure, and in-house teams now run it.
• A PE-backed SaaS client scaled from 1 customer to 1,000 in 9 months without a rewrite.
• Roche gained a continuous delivery solution in a 2-month engagement.
• DSM-Firmenich’s Scentmate system reached 99.95% stability.

Exxeta

• Founded: 2005
• Legacy Expertise: COBOL, RPG, monolithic legacy systems, on-premises data centres
• Primary Tech Stack: AWS, Azure, Google Cloud, Spring Boot, Angular, GraalVM
• Engagement Model: Strategy and assessment, pilot and execution, managed transformation

Exxeta replaces system landscapes that run on COBOL, RPG, and other legacy solutions through a Decompose, Transform, Synthesize method with agent-supported migration. The exxfer platform uses AI to detect architecture smells and identify microservice candidates inside monoliths, with a published 25% faster delivery.

Programs run through strategy and assessment, pilot and execution, and managed transformation, and larger landscapes usually take 12 to 24 months. On a Mercedes-Benz Java Reloaded project, a move to GraalVM and AWS Lambda cut server costs by 99%.

Delivery highlights

• MLP Finanzberatung left in-house data centres for Google Cloud Platform, and only 8 of 473 support tickets fell outside the target resolution time.
• Mercedes-Benz Leasing runs a new leasing platform on Alfa software in the public cloud.
• Remote Configuration for Mercedes me runs on Spring Boot microservices.
• 1,200+ employees work across 14 locations.
• Microsoft Solutions Partner status and a Databricks partnership support cloud work.
• Individual systems often reach a modern stack in a few months.

ELCA

• Founded: 1968
• Legacy Expertise: Mainframes, monoliths, three-tier applications, Teradata warehouses
• Primary Tech Stack: Cloud-native microservices, Azure integration services, AWS, Snowflake, Camunda
• Engagement Model: Fixed-price or time-and-materials projects, managed teams, product co-development

ELCA delivers modernization as fixed-price or time-and-materials projects, through managed teams, or as product co-development with partners. Options range from encapsulation and rehosting to refactoring, rearchitecting, rebuilding, or replacement, moving mainframes to cloud and monoliths to microservices.

For Sommet Education, an Azure Business Integration Platform replaced a legacy student system across 5 institutions and 20 campuses. Certifications span ISO 9001, 14001, 27001, 27017, 27018, and 27701, and sovereign hosting runs through ELCA Cloud Services.

Delivery highlights

• GF Machining Solutions runs an Azure AI knowledge system for 550+ field service engineers handling 100,000+ tickets a year.
• swisspor built a Snowflake and Power BI platform with dbt and Terraform.
• Viacar AG modernized a core application from the 1990s under a partnership that dates to 2015.
• A dedicated offering moves Teradata warehouses to AWS.
• 2,150+ employees work across onshore, nearshore, and offshore centres.
• Partners include Microsoft, AWS, Databricks, Snowflake, ServiceNow, and Camunda.

Siili Solutions

• Founded: 2005
• Legacy Expertise: On-premises CMS platforms, fragmented web estates, legacy applications
• Primary Tech Stack: AWS, Azure, Google Cloud, .NET Core, React, Dynamics 365
• Engagement Model: Managed services, nearshore delivery, advisory

Siili Solutions covers rehost, replatform, refactor, rebuild, and replace paths in an AI-powered modernization offer, with a Legacy Code Analyzer that targets 40% to 60% faster discovery and analysis. Published targets also include 30% to 50% lower software development costs and 90%+ automated test coverage.

For Terex, a consolidation of 60+ websites across 14 brands brought a threefold reduction in total cost of ownership and 40% more website visits. As a listed company, the group reported €108.1 million in revenue for 2025.

Delivery highlights

• HMS Networks moved 5 websites and 1,960 products onto one platform and saw 94% more contact-form leads.
• Managed Cloud covers AWS, Azure, and Google Cloud with 24/7 support.
• 100+ certified cloud, data, security, and DevSecOps professionals staff the cloud practice.
• Application Care and Managed AI round out the managed services line.
• Cloud cases include Teosto, SSAB, and Elisa Viihde.
• 21 offices operate in 8 countries.

Evozon

• Founded: 2005
• Legacy Expertise: Perl ETL systems, Rackspace-hosted and on-premises infrastructure
• Primary Tech Stack: AWS, Java, Spring, SAP Commerce, Next.js, PostgreSQL
• Engagement Model: Proof-of-concept start, DevOps and managed services

Evozon re-platformed the Un-Doi bill payment network onto AWS with zero downtime, and daily transactions grew from under 10,000 to over 140,000. For Tires-Easy, an assess, mobilize, migrate, and modernize framework moved the retailer from Rackspace to AWS with 50% lower infrastructure costs.

On the code side, a 3-person team rewrote a 4-year-old Perl ETL system in 9 months. Cloud work starts small with proof-of-concept projects, backed by AWS Advanced Tier Services Partner and Microsoft Gold Partner status.

Delivery highlights

• 500+ experts bring 20+ years of custom software experience.
• Tires-Easy tracks inventory across 1,100+ warehouses in real time.
• Un-Doi handled a peak of 21,000 transactions in a single hour.
• IBM Business Partner and SensioLabs Bronze Partner status extend the partner base.
• Named clients include IBM, Auchan, Banca Transilvania, and Adobe.
• Services span cloud consulting, cloud migration, DevOps, and managed services.

Phases of a Legacy Modernization Roadmap From Audit to Go-Live

A modernization program runs best as a series of small, reversible steps, each with an exit point and a clear owner. When you plan the roadmap this way, your operations keep running, and your budget shows results long before the final cutover. Here are the 5 phases of a roadmap that keeps systems live:

Phase 1. Discovery and System Mapping

Discovery turns an undocumented system into a map you can plan against. The team inventories code, integrations, data flows, batch jobs, and the business rules that live inside old modules, then interviews the people who still know why each rule exists. From there, every module gets a decision: rehost, replatform, refactor, re-architect, or rebuild. Your output is a risk register, a dependency map, and a first estimate you can take to finance.

Phase 2. Target Architecture and Business Case

This phase decides where the system will land and what the move has to pay back. Your architects and the vendor agree on a target that fits your compliance load as well as your traffic:

• Cloud platform and region, with EU data residency where GDPR applies
• Service boundaries for the parts you will split out of the monolith
• Data stores for each workload, from relational databases to document stores
• Security and resilience controls that match DORA or NIS2 if your sector falls in scope
• KPIs and a budget envelope that finance signs off before build work starts

Phase 3. Pilot Migration on a Low-Risk Module

A pilot proves the whole delivery chain on one bounded module, such as a reporting service or an internal admin tool. You see the CI/CD pipeline, automated tests, data sync, and rollback working in production conditions before the high-stakes modules move.

Measure release time, defect rate, and cloud spend during the pilot, because those numbers become the baseline for every later wave. If the pilot exposes gaps, your team fixes them while the cost of change stays small.

Phase 4. Phased Rollout With Parallel Running

Rollout moves the system module by module while the legacy version keeps serving users. You keep a working fallback at every step, and your customers keep working through each cutover:

• Strangler-fig routing sends traffic for each migrated function to the new service
• Two-way data sync keeps old and new databases consistent during the overlap
• Feature flags let your team switch users between versions in minutes
• Cutovers happen in low-traffic windows with a rehearsed rollback plan
• Retirement of each legacy module follows once usage drops to zero

Phase 5. Post-Launch Optimization

Go-live opens the phase where the savings show up. The team switches off old servers and licenses, tunes cloud capacity to real usage, and sets alerts on the KPIs from Phase 2. Your engineers receive the documentation, runbooks, and architecture records, so you keep full control of the platform after the vendor steps back. After handover, a light support retainer or a lean in-house team can carry the system forward.

Tips for Picking the Top Legacy Software Modernization Companies in Europe

You learn the most about a modernization partner from what they do before the contract, when a small piece of real work shows how the team thinks. Here are 5 tips for testing a vendor before you sign:

Start With a Paid Assessment

A short paid assessment gives you a real deliverable to judge before you commit to a multi-year budget. Ask for a written roadmap, a module-by-module decision, and a cost range, and treat the quality of that document as a preview of the whole engagement. Firms that skip a paid first step, or offer only a free sales audit, give you less to compare.

Ask for Cases on Your Own Stack

Your shortlist gets sharper when each vendor shows work on the same technology and sector you run. Make sure references match on these points:

• Source platform, such as .NET Framework, Java EE, COBOL, or Delphi
• Target cloud and the services the team used there
• Sector rules that applied, from GDPR to DORA
• Scale in users, transactions, or data volume
• Results the client confirms in a public review or a reference call

Check How the Team Keeps Systems Live

Downtime during migration hits revenue and customer trust at once, so ask every vendor to walk you through a past cutover step by step. Listen for parallel running, data sync, rehearsed rollbacks, and the metrics they watched during the switch. A clear answer names an incident they handled and what changed in their process afterwards, and that level of detail gives you a realistic view of your own cutover.

Meet the Engineers Who Will Do the Work

The people in the pitch meeting and the people in your sprint reviews often differ, so meet the delivery team before you sign. Use that session to confirm the basics:

• Named lead engineer and architect for your project
• Certifications on the target cloud, such as Azure or AWS
• Experience with the legacy language in your codebase
• Overlap of working hours with your in-house team
• Replacement terms if a key person leaves mid-project

Probe How They Recover Undocumented Business Rules

Legacy code often holds decades of business logic that nobody wrote down, from tax rounding rules to exceptions for your largest customer. Ask how the vendor extracts those rules: code analysis tools, AI-assisted software development practices, interviews with long-serving staff, and test suites that lock in current behavior before anyone changes it. A vendor with a concrete method protects you from the classic failure where the new system runs faster and calculates the wrong invoice.

Conclusion

Legacy software modernization means moving the systems your business already depends on onto a stack your team can change, secure, and scale. The risk sits in the parts nobody owns: business rules without documentation, integrations no one mapped, and cutover plans that exist only on a slide. When those gaps stay unowned, they surface as delayed releases, failed audits, and weekends lost to rollback.

The right partner owns those gaps from the first assessment: they map the system, put a price on each decision, and keep your operations live while modules move one at a time. A poor fit pushes a big-bang rewrite and leaves you to absorb the risk. Among the top legacy software modernization companies in Europe, look for the team that shows you this plan in writing before you sign and stays accountable for it after go-live.