Drawing on debates in lesbian and gay periodicals and writings from and about post-structuralist ''queer theory'' and politics. this paper clarifies the meanings and distinctive politics of ''queerness,'' in order to trace its implications for social movement theory and research. The challenge of queer theory and politics, I argue, is primarily in its disruption of sex and gender identity boundaries and deconstruction of identity categories. The debates (over the use of the term ''queer'' and over bisexual and transgender inclusion) raise questions not only about the content of sexuality-based political identities, but over their viability and usefulness. This in turn challenges social movement theory to further articulate dynamics of collective identity formation and deployment. While recent social movement theory has paid attention to the creation and negotiation of collective identity, it has not paid sufficient attention to the simultaneous impulse to destabilize identities from within. That tendency, while especially visible in lesbian and gay movements, is also visible in other social movements. It calls attention to a general dilemma of identity politics: Fixed identity categories are both the basis for oppression and the basis for political power. The insights of bath sides of the dilemma highlighted here raise important new questions for social movement theory and research.