The gay and lesbian liberation movement and its predecessor, the homophile movement that originated in the 1950s, have been relatively little studied by sociologists; yet theories of ethnic mobilization, especially competition theory, help us to understand the mobilization of lesbians and gay men. At the same time, lesbian/gay social movement activity provides an important critique of social movement theories. This article focuses on the Daughters of Bilitis, a homophile organization for women founded in 1956. Competition theory furnishes a useful framework (...) for understanding the transformation and decline of the DOB and its publication, the Ladder, at the end of the 1960s, but it cannot fully explain lesbian social and political organization. By viewing group identities as multiple and overlapping, new social movement theory contributes a more complete understanding of the Daughters of Bilitis and its relationship to other social movement groups in the late 1960s and early 1970s. (shrink)