This guide outlines the process of application modernization, detailing the steps necessary to envision, plan, and execute modernization initiatives effectively. It begins by introducing the Gartner® TIME framework, which is utilized for rationalizing the application portfolio to identify candidates for modernization. The document emphasizes the importance of assessing both functional and technical fit of applications to determine their suitability for modernization. Following this, the guide presents the 6R method, which includes replace, re-architect, re-platform, rehost, retain, and retire, as a structured approach to decide on the next actions for specific applications. The guide also discusses potential barriers to modernization and highlights the role of SAP LeanIX in supporting the modernization process. It concludes by emphasizing the benefits of application modernization, such as improved efficiency, enhanced security, and increased business agility, while also addressing the risks associated with legacy applications.