Abstract—Modernization and migration initiatives are not limited to projects where complex legacy systems need to be phased-out. They include wider contexts, from the replacement of obsolete middle tiers, to the migration of algorithms from prototype-purpose platforms to commercial platforms. As the need of modernization continues to increase, we need to understand better what are the challenges to be addressed in relation to modern practices and processes. Aspects such as: decision-making on the migration of components/sub-systems, management of operations during the phase-out stages, critical knowledge and business logic transfer, they all impose demands on the development cycle and the way in which projects are planned and carried out. This paper presents a synopsis of challenges encountered during several modernization and migration initiatives within different industrial domains, across organizations spanning diverse countries. Some key lessons learned were: (1) work planning needs to be adjusted to handle better information uncertainty, (2) estimation practices need to be fine- tuned, e.g., by explicitly allocating information foraging activities prior estimation activities, (3) documentation and traceability cannot be neglected, (4) the phenomenon of ‘role creep’ should be avoided, and finally (5) clear processes need to be in place for the procurement of appropriate test data, and for enabling test automation.