 The subject of transworld identity has been highly contentious, even among philosophers who accept the legitimacy of talk of possible worlds. Opinions range from the view that the notion of an identity that holds between objects in distinct possible worlds is so problematic as to be unacceptable, to the view that the notion is utterly innocuous, and no more problematic than the uncontroversial claim that individuals could have existed with somewhat different properties. Matters are complicated by the fact that an important rival to ‘transworld identity’ has been proposed: David Lewis’s counterpart theory, which replaces the claim that an individual exists in more than one possible world with the claim that although each individual exists in one world only, it has counterparts in other worlds, where the counterpart relation (based on similarity) does not have the logic of identity. Thus much discussion in this area has concerned the comparative merits of the transworld identity and counterpart-theoretic accounts as interpretations, within a possible-worlds framework, of statements of what is possible and necessary for particular individuals. (Similar issues arise concerning the  transworld identity of properties.)