We all know when a familiar object is not usable: a pen with no ink cannot be used for writing in a notebook and a scratched photo lens will not produce a good picture. Objects can become unusable because of breakages, missing parts or flat batteries. Alternatively, an object may have been so badly designed that it was never of much use in the first place. In either case, this is ‘usability’ in its most basic definition: whether something can be used for its intended purpose. However, as this chapter will try to show, in mobile learning this basic level of usability (it works/it doesn’t work) cannot be taken for granted. What is more, this basic level is often not enough for understanding complex devices, the demands of educational activities and the needs of hurried lifestyles.