Advances in technology, changing customer requirements, and pressure from business goals are the main drivers for innovation in the banking industry. Legacy architectures with monolithic structures prevent banks from implementing new generation banking models. To stay competitive, banks migrate to modular and scalable architectures. This migration has a significant impact on banks’ technical and organizational infrastructures, so it is crucial to devise an end-to-end migration strategy and plan the transformation. This paper reports our observations on the legacy system migration of three large retail banks between 2014 and 2020, focusing on the evaluation and prioritization criteria for their application portfolio to be migrated. We compare and contrast the motivations, migration strategies, and migration prioritization methods and discuss key takeaways from these high scale migration projects.