Something that always surprises me when I try to discuss what I write about is that a lot of people do not understand what a fictional crossover is. I felt that before reading the Television Crossover Universe, I had best explain what it is.
The term crossover can be used in a very general way, or in a more specific way.
In a broader sense, a crossover can be any combination of two separate series. This can include mashups. An example of this would be a story or even a picture with Dirty Harry Potter, combining the character of Dirty Harry played by Clint Eastwood with the boy wizard from the J.K. Rowling books.
It can also be a story that couldn’t possibly exist within the canon of the series involved. One example was the Cartoon All-Stars to the Rescue animated special. This combined many famous cartoon characters, but presented them all as toys brought to life.
For my purposes, what I consider to be a valid crossover is one where two series are combined in a way that demonstrates that both series separately coexist within the same shared reality. Who Framed Roger Rabbit is one great example of this. Several cartoon characters from several different animation studios owned by different companies appeared within the same story, in a manner that did not contradict their individual canons. Thus, we were able to deduce from the evidence of the film that characters like Mickey Mouse and Bugs Bunny actually existed in the same universe, even if they had seldom crossed paths.
In the live action world of television, crossovers are used often as marketing gimmicks. A great way to get people to watch a new show is to have a character from a more well known series appear. Detective Munch was a character from Homicide, who guested on Law & Order, and then became a regular on Special Victims Unit. He also appeared on X-Files and Arrested Development. Thus, all of those shows coexist in the same reality. The Bluth family lives in a world where Mulder is uncovering conspiracies because of Detective Munch.
Of course, crossovers can be more subtle. Angel is in the same universe as Buckaroo Banzai and the Alien franchise because the fictional companies from those series are clients of the law firm from Angel. Fictional companies and products, such as Oceanic Airlines or Morley Cigarettes, can provide a link to add series to a shared reality.
For more specific examples of what counts and doesn’t count as valid crossovers for the purposes of my writing projects, see tomorrow's post on Television Crossover Universe Rules for Inclusion in the Television Crossover Universe.