It is widely believed that to be a conspiracy theorist is to suffer from a form of irrationality. After considering the merits and defects of a variety of accounts of what it is to be a conspiracy theorist, I draw three conclusions. One, on the best definitions of what it is to be a conspiracy theorist, conspiracy theorists do not deserve their reputation for irrationality. Two, there may be occasions on which we should settle for an inferior definition which entails that conspiracy theorists are after all irrational. Three, if and when we do this, we should recognise that conspiracy theorists so understood are at one end of a spectrum, and the really worrying form of irrationality is at the other end.