2000 AD crossovers are crossover stories appearing in British comic 2000 AD, its sister title the Judge Dredd Megazine, and other related output, such as novels, audio plays, films and role-playing games.

Not all of the stories told in 2000 AD and its related publications exist in the same shared universe, unlike in some other comics, for example, the DC and Marvel Universes. Indeed the majority of stories which have appeared in 2000 AD since 1977 have never been connected with each other. However, the series which are so connected are generally the most significant ones in the comic in terms of the number of issues they have appeared in, their popularity with readers, and their significance in the history of the comic.

Those 2000 AD stories which occupy a shared universe and have crossed over with each other include:

Series can be linked to each other in either of two ways: crossovers and spin-offs. There are also combinations of both.

Firstly, series which were completely independent of each other when they were created – often by different writers, and sometimes even in different comics – were later linked to each other. This could be done either by a crossover story in which two or more characters from the respective series meet each other, or by a caption or piece of dialogue explicitly referring to events which occurred or characters who appeared in an earlier story in another series. Two examples of the former kind are the Judge Dredd stories "Top Dogs" and "Judgement Day", which both featured Johnny Alpha from the series Strontium Dog in a major role. Alpha lived over half a century in Dredd's future, and the crossover was accomplished by having Alpha time-travel back to Dredd's era. An example of the second kind is the Judge Dredd story "The Cursed Earth," which featured a dinosaur called Satanus who was described as the clone of the offspring of the female dinosaur which had appeared in most episodes of the earlier series Flesh. Flesh was a previously unconnected series about humans time travelling back to the Cretaceous era to harvest dinosaurs for their meat.

Sometimes the link between two series can be of paramount importance to the story (such as Alpha's appearance in Judge Dredd); in other stories the reference can be a passing homage to an earlier tale with no effect whatsoever on the plot of the story in which it occurs (such as the reference to Satanus' ancestry in "The Cursed Earth"). In either case, once a connection between two series was established, it was often repeated. For example, "Top Dogs" was followed up by "Judgement Day," and the reference to Flesh in Judge Dredd was reciprocated by the cameo appearance of a Mega-City judge in Nemesis the Warlock Book V, which was itself a crossover with Flesh because it featured Satanus in a major role.

This latter example illustrates how series were not just linked to each other in pairs, but in multitudes. Pat Mills, the first editor of 2000 AD and creator of many enduring series, was responsible for many such connections. He deliberately connected his own series ABC Warriors to Flesh, and then linked Nemesis to both. (All three series were created by him, but they had originally had nothing to do with each other.) For example, ABC Warriors made a passing reference to a dinosaur being the son of Satanus. Satanus himself subsequently played an important part in Nemesis Book V, by which time the entire cast of ABC Warriors had themselves moved to the Nemesis strip. This therefore established that Judge Dredd, Flesh, Nemesis, and ABC Warriors all existed in the same continuity: a list which would be added to many more times.

Secondly, a new series can be created as a deliberate offshoot from a parent series. This can also occur in two ways. One method was to take a supporting character from an existing series and start a new series with that character in the lead (sometimes with the lead character from the original series appearing in a cameo). Two examples are Judge Anderson, first introduced in Judge Dredd, being given her own series, Anderson: Psi Division, five years later; and Durham Red getting her own series after her debut in Strontium Dog. Since Judge Dredd and Strontium Dog occupy the same universe, it follows that Anderson and Red do too (although they have never both appeared in the same story).