Regions across the United States have developed sustainability plans and programs funded through the U.S. Department of Housing and Urban Development's (HUD) Sustainable Communities Initiative (SCI). The SCI program was an experiment in regional sustainability planning in which grantees received federal awards in 2010 or 2011, with HUD providing funding and technical assistance to grantees through 2015. HUD designed the program to increase cooperation between regional actors whose activities, such as housing, transportation, and economic development, typically occur in different policy "silos." The program promoted the incorporation of social equity frameworks and metrics into economic and environmental sustainability-related activities, areas in which there are benefits to taking a regional approach.The HUD-SCI program provides an opportunity to assess how regions incorporate equity into plans and inform the next generation of regional planning. California is a particularly interesting site for assessing the success of the HUD-SCI program in promoting regional cooperation and social equity because of SB 375, a state law mandating regional sustainability planning. This paper assesses the variation across regions within California in incorporating social equity into HUD-SCI grant planning activities. It does this by presenting three case studies of the role of social equity in regional sustainability planning in the Sacramento metropolitan area, the San Francisco Bay Area, and the Fresno region of the Central Valley.This paper fills a gap in the sustainability governance literature by providing insight into how equitable the regional sustainability planning process is. The urban design literature on sustainability is largely prescriptive (Calthorpe and Fulton 2001), proposing compact urban form without assessing how agencies with varied responsibilities in regions incorporate equity into sustainability plans (Berke and Conroy 2000; Jepson and Edwards 2010). The literature on regional planning is largely descriptive, explaining the conditions under which regional agencies can cooperate to achieve regional goals, with or without federal incentives (e.g., Seltzer and Carbonell 2011). Regional equity scholarship, with its strong focus on social movements, would benefit from a better understanding of the planning and governance processes that these movements seek to shape (Pastor, Benner, and Matsuoka 2009). The inherent tensions in balancing the three Es, equity, environment, and the economy (Campbell 1996), with competing stakeholder perspectives and interests, complicates regional sustainability planning.2 Despite these challenges, many are optimistic about the future of regional sustainability planning (Chapin 2012;Chapple 2014). Regional sustainability planning is an opportunity to accommodate growth through compact development, while avoiding the socially inequitable outcomes of past federally subsidized projects of urban renewal and suburbanization (Chapin 2012). Chapin calls for more nuanced research on the po...