"Collective impact" is a new place-based model of educational and social intervention that aims to shift responsibility for improvement in outcomes from individual organizations to entire systems that affect the lives of people in a particular location. CCRC's "Corridors of College Success Series" provides insights into collective impact efforts in the postsecondary sector, drawing on qualitative research in five communities participating in the Ford Foundation's Corridors of College Success initiative. The Ford Foundation supported these communities as they planned, organized, and applied a collective impact or place-based approach in order to improve pathways into and through college and into family-sustaining careers for low-income and first-generation students and other vulnerable populations. This brief provides an introduction to the collective impact model and the Corridors of College Success initiative. Subsequent briefs in the series will focus on key areas of concern for practitioners, policymakers, funders, and researchers engaging in place-based collective work--including implementation issues, "backbone" organizations, postsecondary engagement in collective impact, funders and funding, and community voice.