This chapter discusses performance as one of the main qualitative characteristics of a mobile application. It focuses on the limitations of mobile applications in different circumstances. This chapter explores appropriate usage of memory and storage and emphasizes the speed of performing any task or action. It discusses the application availability when needed and mainly focuses on the ability of the application to process many tasks. Besides, it explores how the application can deal with the long-time loading and focuses on the appropriateness of application feedback. Finally, this chapter explores how an application can scale up, scale down, or scale-out.