Developing cross-platform mobile applications as well as migrating existing native applications to other platforms are complex tasks where developers have to face numerous issues. In this thesis we analyze challenges and existing approaches related to cross-platform development and focus specifically on the migration of existing native mobile applications to other platforms. The purpose is to explore existing approaches to cross-platform mobile application development and define whether and how these approaches can be used for migration of legacy applications. As result, a generic method for migrating legacy applications to other platforms has been developed. In order to provide a proof-of-concept, the migration method has been applied to a case-study in industrial settings where the legacy applications were developed for windows 8.1 tablets. The chosen cross-platform development tool for migration in the case-study was Xamarin and a prototype for the platforms Android and iOS were implemented.