Open Educational Resources (OER) are free learning resources available on the Internet. OER can be openly licensed or in the public domain, and can be used or reused for free. They can exist in many formats: text (either print or digital); audio, video, multimedia or hypermedia; or various combinations of these. They can be based on a single learning point, a lesson, a series of lessons (a module), a whole course or even an entire programme of study. They can support a specific learning methodology or approach — whether that be behaviourist, constructivist, connectivist, etc. — or any combination of methodologies or approaches. Although they may differ in format, structure or approach, they share a common characteristic: their openness. The Knowledge Series is a topical, start-up guide to distance education practice and delivery.