Mobile learning may be defined either by the device constraints of the learner (e.g., a mobile phone) or by the context in which the learner is situated (e.g., sitting on the bus on the way to work). While the former may be the more common conception, the latter is becoming an increasingly important design consideration. This entry first describes how mobile learning has evolved along with changes in devices. It then discusses the affordances of mobile learning and the opportunities and constraints of learning on mobile devices.