This chapter discusses the usability of a mobile application as one of the main qualitative attributes. The chapter focuses on the users’ expectations about usability and the redundancy of content or appearance of the product. It discusses how fast and easy it to learn the use of the mobile application is by memorizing what has been learned from the application. Moreover, it emphasizes the application's capabilities to recover the required information. It discusses how experienced mobile users can perform common tasks very fast and the possibilities of interacting with other applications. This chapter emphasizes protection against making mistakes and meeting the accessibility standards, which apply to the mobile application.