In superhero comic books, a team-up is a fictional crossover where two superheroes or superhero teams who usually do not appear together work together on a shared goal.
Team-ups can either happen within one of the character's main series or in the team-up's separate series. Team-up series generally work in one of three ways: the same characters teaming up every issue, one character teaming up with a rotating second character, or two different characters teaming up every issue.
A recurring theme of team-ups is when two superheroes meet for the first time, they might argue with or even fight each other.