Abstract
Legacy system migration has emerged as one of the most complex and consequential challenges in contemporary information systems engineering. As organizations confront mounting pressures arising from digital transformation, regulatory compliance, cybersecurity threats, and escalating operational costs, the modernization of entrenched software systems has become unavoidable. This research article presents an extensive and theoretically grounded investigation into the architectural, methodological, and organizational dimensions of legacy system migration, with particular emphasis on the evolution from ASP.NET to ASP.NET Core as a representative case of platform-level transformation. Drawing on a broad and interdisciplinary body of literature, the study situates ASP.NET Core within wider discourses on cloud-native architectures, microservices, hybrid migration strategies, automation, and risk-based decision-making. Central to the analysis is the recognition that technical migration is inseparable from organizational culture, governance models, and human capital considerations. The article adopts a qualitative, interpretive research design grounded in comparative literature synthesis and conceptual analysis. The findings highlight that successful migration outcomes are contingent upon aligning architectural decisions with socio-technical realities, including legacy knowledge embedded in monolithic systems, institutional resistance to change, and evolving skill requirements. Particular attention is given to tooling ecosystems, implementation strategies, and incremental modernization pathways articulated in recent scholarship, including the evolution of ASP.NET Core as a modular, cross-platform, and performance-oriented framework (Valiveti, 2025). The discussion advances a multi-layered theoretical model that integrates architectural evolution, organizational readiness, and strategic governance, while also addressing limitations and unresolved debates in the field. By offering a deeply elaborated and critical perspective, this article contributes to both academic scholarship and practitioner discourse on sustainable and resilient legacy system modernization.