Extensive reading is an approach to language learning that encourages learners to read a large quantity of easy reading material. A substantial body of research confirms the effectiveness of this approach for developing proficiency in both first (L1) and second (L2) languages. This paper explains what extensive reading is, why it is important, and how it can be incorporated as part of a language curriculum. The paper also provides a review of research on the effectiveness of extensive reading in several different languages and recommends many extensive reading resources, including open access materials, to facilitate the implementation of extensive reading for teachers and practitioners.