A conspiracy theory is an allegation that a certain event or events are secretly influenced by a premeditated group or groups of powerful people or organizations working together.

Conspiracy theory may also refer to:

Conspiracy theory (legal term), a theory of a case that presents a conspiracy to be considered by a trier of fact

Conspiracy Theory (film), 1997 film starring Mel Gibson and Julia Roberts, directed by Richard Donner

Conspiracy Theory with Jesse Ventura, TV series hosted by former Governor of Minnesota Jesse Ventura

Conspiracy Theories, 2006 progressive jazz album by Phil Miller's In Cahoots