In recent years, the cloud hype has led to a multitude of different offerings across the entire cloud market, from Infrastructure as a Service (IaaS) to Platform as a Service (PaaS) to Software as a Service (SaaS). Despite the high popularity, there are still several problems and deficiencies. Especially for PaaS, the heterogeneous provider landscape is an obstacle for the assessment and feasibility of application portability. Thus, the thesis deals with the analysis and improvement of application portability in PaaS environments. In the course of this, obstacles over the typical life cycle of an application - from the selection of a suitable cloud provider, through the deployment of the application, to the operation of the application - are considered. To that end, the thesis presents a decision support system for the selection of cloud platforms based on an improved delimitation and conceptualization of PaaS. With this system, users can identify offerings that enable application portability. For validation, a case study with a real-world application is conducted that is migrated to different cloud platforms. In this context, an assessment framework for measuring migration efforts is developed, which allows making the differences between compatible providers quantifiable. Despite semantically identical use cases, the application management interface of the providers is identified as a central effort factor of the migration. To reduce the effort in this area, the thesis presents a unified interface for application deployment and management. In summary, the work provides evidence of application portability problems in PaaS environments and presents a framework for early detection and avoidance. In addition, the results of the work contribute to a reduction of lock-in effects by proposing a suitable standard for management interfaces.