Mobile learning has been a research topic for some 20 years. Over that time it has encompassed a wide range of concepts, theories, designs, experiments and evaluations. With increasing interest in mobile learning from researchers and practitioners, an accessible overview of this area of research that encapsulates its many facets and features can provide a useful snapshot of the field to interested parties. This article provides a summary of the field of mobile learning, applying the main analysis categories of research, technology, content, learning and learner. The author presents these categories and subcategories in the form of a mind map, which outlines the details of the major themes in mobile learning. In addition, the author contextualises the key developments in mobile learning in a timeline. The intent of this article is that it may serve as an introduction to the research field of mobile learning, enabling researchers to quickly familiarise themselves with the type of work that has been done in the past, and the potential areas of investigation that might prove fruitful in the future.