This chapter discusses the capability of a mobile application as one of the main qualitative characteristics. The chapter focuses on the completeness of the mobile application and the availability of all important functions. The features of accuracy and the efficiency of performance in mobile applications are explored and discussed. This chapter focuses on the best way in which the different features interact with each other and discusses the ability to perform multiple parallel tasks at the same time. Besides, this chapter pays emphasis to the support provided to all possible data formats. Finally, it discusses the ability to add features or change the current behavior of the application.