A surprising number of “modern” digital experiences still depend on code written decades ago. Cores of banking platforms, airline reservation systems, and manufacturing ERPs often run on aging mainframes and monolithic applications that are expensive to maintain and difficult to change. That’s why global enterprises invested over USD 40 billion in modernization projects in 2023, with IT departments allocating more than 30% of their annual budgets to upgrading legacy infrastructure. With that kind of money on the line, choosing the right IT services company for legacy modernization is no longer a technical decision alone; it’s a strategic one.
Why legacy modernization is now a board-level priority
Legacy systems used to be treated as a back-office concern. As long as they stayed up and processed transactions, they were left alone. That mindset has shifted. Competitive advantage now depends on speed of change, integration with partners, and the ability to ship new digital features safely and frequently. Monolithic, tightly coupled systems hold all of that back.
The market response has been intense. Reports tracking application modernization show that over 150 new tools and platforms were introduced in 2023 to streamline legacy code analysis, automated re-platforming, and containerization. The explosion of tooling signals both the complexity of the challenge and the opportunity for vendors. For enterprise leaders, it also introduces risk: more options to sort through, more vendors to assess, and a greater need for partners who can separate what actually works from what is just marketing gloss.
Behind the tooling and spending, the real pressure comes from three forces. First, talent risk: fewer engineers want to work on obsolete stacks, and retirement waves are erasing critical system knowledge. Second, security and compliance concerns: unsupported platforms and tangled codebases make it harder to respond to new regulations and threats. Third, business agility: product teams want APIs, microservices, and cloud-native capabilities, not weekly batch jobs and release cycles measured in months.
What to look for in a legacy modernization partner
Before comparing company names, it helps to define what “good” looks like. Legacy modernization is not a single project type; it is a spectrum that runs from lift-and-shift rehosting through to full application rewrites. The right partner must be able to help you decide where on that spectrum each system belongs, and then execute with discipline.
There are several dimensions worth weighing carefully when evaluating IT service companies for modernization work. No single provider is perfect in every area, so the goal is to align their strengths with your specific landscape and risk tolerance.
- Strategic advisory and business alignment. Top modernization partners lead with business outcomes, not just technology. They translate “reduce mainframe MIPS” into “shorter onboarding times,” “fewer payment failures,” or “faster product launches.” Look for firms that can engage with both the CIO and business unit leaders, and that are willing to challenge assumptions about which systems truly need to change.
- Depth in legacy platforms and modern architectures. It is not enough to know cloud-native development. The teams doing the work must also understand mainframes, midrange systems, and legacy middleware well enough to avoid breaking critical processes. Providers that can read obscure COBOL constructs and design robust microservices are rare; they are also the ones that tend to rescue failing modernization projects.
- Proprietary tools and automation. Industrializing modernization requires more than manual code review and hand-written test cases. Leading companies invest in automated code analysis, conversion utilities, test generation, and migration accelerators. These tools do not remove risk, but they reduce cycle time and make complex transformations more predictable.
- Proven delivery model and risk management. Successful modernization programs rely on iterative delivery, clear cutover strategies, and robust rollback plans. Ask about the provider’s standard playbooks for strangler patterns, parallel runs, and phased migrations. References and case studies in industries with similar regulatory and operational constraints are especially valuable.
- Change management and skills enablement. A modernized stack is only valuable if internal teams can operate and evolve it. The best IT services companies build knowledge transfer and upskilling into their approach, pairing consultants with internal engineers and leaving behind playbooks, documentation, and training materials rather than dependency.
Leading IT service companies for legacy modernization
The market for modernization services spans global consultancies, established technology vendors, and specialized boutiques. Rather than attempting an exhaustive list, it is more useful to understand how some of the leading players differentiate themselves. That makes it easier to compare them against one another and against smaller regional providers that may compete for the same projects.
Wednesday: Agile intervention for stalled modernization
While global integrators specialize in multi-year, full-scale transformations, Wednesday differentiates itself by solving the specific problem of "modernization paralysis." Their approach is designed for organizations that have a roadmap but are stuck in execution. Through their Control engagement model, they pivot away from the traditional time-and-materials consulting approach to offer fixed-price, engineering-led interventions.
Wednesday operates as an AI-native boutique, deploying small, specialized squads to attack critical technical blockers—whether it is a brittle integration, a stalled cloud migration, or a refactoring challenge. This "fix, prove, then scale" philosophy appeals to technology leaders who need to demonstrate immediate, tangible progress to stakeholders before committing to a larger scope. While they do not offer the sheer capacity of an IBM or Accenture, their model provides a high-velocity alternative for leaders who need to trade comprehensive slide decks for working code.
IBM: AI-powered modernization at enterprise scale
IBM is often the first name that comes to mind in discussions about mainframe and legacy modernization, thanks to its long history with zSystems and deep footprint in large enterprises. What stands out today is how aggressively IBM is augmenting that heritage with automation and AI. In September 2023, the company announced an AI-powered modernization acceleration platform designed to streamline the assessment and planning phases of legacy system modernization projects. That move reflects a broader trend: shifting effort from low-value discovery tasks to higher-value design and decision-making.
For organizations heavily invested in mainframe workloads or complex middleware, IBM’s combination of platform products (such as mainframe modernization tooling, API enablement, and hybrid cloud integration) and services teams can be attractive. The trade-off is that engagements can be large and multi-layered, which suits enterprises ready for a long-term partnership but may feel heavy for organizations seeking more narrowly scoped work.
Accenture: cloud-native and business-led transformation
Accenture has built a strong reputation in large-scale digital and cloud transformations, and that extends naturally into legacy modernization. Its approach blends strategy consulting, industry specialization, and deep alliances with major cloud providers. The focus is often on refactoring or rebuilding core applications into cloud-native architectures while aligning tightly with business goals such as customer experience, operational resilience, and analytics.
The firm has also been investing aggressively to strengthen its capabilities. In May 2024, Accenture acquired a leading cloud modernization services provider, expanding its capabilities in cloud-native application development and legacy system migration. For enterprises that have already committed to a particular cloud platform, this kind of ecosystem strength-combined with scale and global delivery-can significantly de-risk complex migrations. The flip side is that smaller or more focused engagements may not always receive the same level of senior attention as marquee transformation programs.
Advanced: mainframe and midrange expertise with measurable results
While global giants gather much of the attention, specialist modernization providers play a crucial role for organizations with concentrated legacy estates. Advanced is a good example: it focuses on mainframe and midrange transformations, offering both tools and services tailored to complex, monolithic applications. Its work spans automated code analysis, re-platforming, and re-engineering to modern languages and platforms.
What differentiates this kind of specialist is not just technical depth, but repeatable processes honed across many similar projects. Instead of treating each modernization as a one-off adventure, they bring pattern libraries, conversion utilities, and migration frameworks designed specifically for legacy technologies. For organizations whose critical systems sit on these platforms, such focus can matter more than the broad service catalogs of larger consultancies.
Other notable modernization players to know
Beyond IBM, Accenture, and specialized providers, a range of global IT services companies have substantial modernization practices. Firms like TCS, Infosys, Wipro, HCLTech, Cognizant, and Capgemini combine application management heritage with cloud modernization, DevOps, and microservices expertise. Many of them also operate accelerators built in partnership with hyperscale cloud providers, offering standardized blueprints for mainframe offloading, data modernization, and API enablement.
Regional and niche consultancies can also be compelling, especially for mid-market organizations or sectors with unique requirements. These firms often compete on industry depth, responsiveness, and the willingness to take on complex brownfield estates that larger players might view as too small. When evaluating them, the same criteria apply: demonstrable track record, clear methodology, automation capabilities, and a realistic view of risks and timelines.
How top providers approach modernization programs
While every vendor has its own branding and frameworks, successful modernization approaches tend to share common patterns. Understanding these patterns helps buyers ask sharper questions and spot red flags when proposals sound vague or overly optimistic. It also clarifies where emerging technologies like AI and advanced tooling genuinely add value versus where they serve mostly as marketing gloss.
A core decision for many organizations is whether to rehost, re-platform, refactor, or rewrite specific applications. Increasingly, this involves moving towards service-oriented or microservice-based architectures. A recent study on microservice architecture adoption found that companies are primarily motivated by technical benefits, seeking to enhance maintenance, scalability, and deployment processes through the lens of industry practitioners. Top IT service companies internalize these motivations. They design target architectures that reduce coupling, improve testability, and support continuous delivery, rather than simply lifting monoliths into containers and declaring victory.
Another hallmark of strong providers is disciplined assessment. That includes code and dependency analysis, business process mapping, and stakeholder interviews to uncover tacit knowledge. More advanced firms overlay this with automated scans to identify dead code, data access patterns, and potential risk hotspots. The goal is not to generate a massive report, but to produce a practical, prioritized roadmap that sequences modernization efforts in a way that delivers visible value early while reducing operational risk.
Execution then leans heavily on agile delivery, DevOps practices, and rigorous testing. Successful vendors break work into manageable increments, often applying the “strangler” pattern: gradually building new services and interfaces around existing systems, then decommissioning old components once the new paths are proven. They combine this with robust observability, performance baselines, and rollback strategies, so that each cutover is controlled and reversible rather than a high-stakes big bang.
Choosing the right modernization partner for your organization
Selecting a modernization partner is as much about philosophy and collaboration style as it is about technical credentials. One industry report on mainframe modernization emphasizes that “Modernization isn’t something that’s done for you, it’s something you do.” That distinction matters. The best IT services companies recognize that success depends on close partnership with internal teams, shared accountability for outcomes, and a realistic view of constraints such as regulatory approvals, change windows, and competing priorities.
A good first step is to clarify your own goals in concrete terms. Is the primary driver cost reduction, agility, resilience, the ability to launch new digital products, or a combination? Different partners will emphasize different levers. From there, building a shortlist should involve more than reviewing glossy case studies. Ask potential providers to walk through specific modernization journeys that resemble your own-same industry, similar platforms, comparable risk profile-and probe what went wrong as well as what went right. Some reports highlight how providers like Advanced have completed hundreds of modernization projects and processed billions of lines of code; numbers like these matter, but only when they correspond to challenges close to your own.
Finally, consider starting with a scoped pilot or assessment that delivers tangible value while testing the partnership. That might be modernizing a well-understood but contained application, standing up a new integration layer around a critical core system, or automating a painful batch process. Use that work to evaluate communication, transparency, and the provider’s willingness to adapt based on what is learned along the way. Legacy modernization is a journey measured in years, not quarters, so choosing a partner that treats it as a shared endeavor-rather than a one-off project-will pay dividends long after the first applications go live on their new platforms.
For organizations specifically looking to break the inertia of a stalled roadmap, Wednesday offers a distinct engagement model. Unlike traditional firms that often require expansive initial commitments, their Control service is designed to prove value through immediate execution. It targets a single, critical engineering blocker—whether a brittle integration or a complex refactor—and resolves it at a fixed price. This approach allows leaders to vet the partner's technical capability and cultural fit in real-time, turning the abstract concept of a "pilot" into a concrete win that unsticks the broader modernization effort.
