In fiction, continuity is often described as consistent linear progression of events seen from the perspective of an outside observer - the audience. Continuity is used to maintain a logical and believable relationship between the objects, people, places, actions, thoughts, motivations and events that make up a work of fiction.

In a broader body of work that encompasses multiple stories set in multiple media requires serial continuity, and in a body of work that involves multiple time periods, metatextuality, and time travel, then rectifying errors or oversights to preserve the willing suspension of disbelief on the part of the observer requires a more complex approach.

In Doctor Who, continuity represents a set of contiguous events set in multiple, but related, universes. It is the framework into which any single work needs to fit, and how well that body of work fits together defines how individual works are regarded by the observer.

Over the years, a number of methods have been used to make better sense of how the Doctor Who universe fits together. Unlike other fictional universes, there has been no consistent or authoritative statement of what is or isn't considered to be part of the 'Doctor Who canon'. In these absence of such an approach, numerous attempts by fans, writers and publishers have been made to define what the Doctor Who canon might be, but the existence of multiple media has led to widespread dissention.

As fans have become the writers and producers of official Doctor Who works, there has been a growing trend of attempting to influence and redefine the rules and fictional facts presented in preceding works.

In some cases, the process used has been blunt and transparent, using definitive statements to retcon events, reinterpreting what has gone before. Other approaches have been more subtle, introducing memes and themes that, in the context of a single piece of work, are open to interpretation. However, when reinforced within a broader body of work, these idea are used to redefine past events, creating the impression that pet theories or ideas have become official.

Another popular conceit is the use of fanwank, introducing continuity references for their own sake, or as a means of making the overall universe seem smaller and more well-connected. Plots driven by past continuity are particularly susceptible to this phenomenon.

But by far the most influential tool in the continuity box is fandom itself. Through the fanzine and fan fiction movements, and through speculation and consensus, both online and in fan groups, a number writers and publishers have inadvertently referenced or included aspects of fanon in official works, establishing popular beliefs and common misconceptions as fictional fact.