Open Educational Resources (OER) – that is, teaching, learning and research materials that their owners make free to others to use, revise and share – offer a powerful means of expanding the reach and effectiveness of worldwide education. Those resources can be full courses, course materials, modules, textbooks, streaming videos, software, and other materials and techniques used to promote and support universal access to knowledge. This book, initiated by the UNESCO/COL Chair in OER, is one in a series of publications by the Commonwealth of Learning (COL) examining OER. It describes the movement in detail, providing readers with insight into OER’s significant benefits, its theory and practice, and its achievements and challenges. The 16 chapters, written by some of the leading international experts on the subject, are organised into four parts by theme: OER in Academia; OER in Practice; Diffusion of OER; and Producing, Sharing and Using OER.