Women and racial-ethnic minorities have had long histories of mobilizing for equality in U.S. society, but recent decades have witnessed an unprecedented expansion in the number and visibility of voluntary and activist organizations committed to challenging gender and racial-ethnic discrimination. What conditions have encouraged this growth? Going beyond more familiar accounts of social movement development, Debra Minkoff uses multivariate techniques to demonstrate that there is an ecology of organizational evolution that has shaped the formation and survival of national women's, African-American, Asian American, and Latino social and political organizations. Changes in the environment for action during the 1960s promoted the creation of a niche for women's and minority organizational activity, and this sector continued to expand even as the climate for social action became increasingly conservative during the 1970s and 1980s. Drawing on recent advances in both social movement and organizational theory and research, Minkoff offers an organizational analysis of the evolution of the women's and racial-ethnic social change sector since the mid-1950s. She provides an original synthesis of social movement and organizational theory, and unique analysis of the development of these women's and minority organizations from the civil rights era to the present.