Faith-based “sanctuary coalitions” (networks of religious groups and organizations which mobilize congregations for the protection of vulnerable immigrants) have increased dramatically in number since the 2016 election. This study uses in-depth case studies of four sanctuary coalitions in Southern California to analyze the effectiveness of their strategies. Leaders of sanctuary coalitions, leaders and participants of the congregations mobilized by the coalitions, and the immigrants who they attempt to protect and serve will be interviewed. The analysis of interview data will 1) identify which strategies have had the most success in protecting vulnerable immigrants 2) identify the primary obstacles to mobilizing congregations to effectively protect immigrants and 3) evaluate which activities and strategies yield the most “return on investment” in terms of their impact relative to money and volunteer hours spent. The analysis will conclude with recommended strategies to help congregations effectively mobilize their members to protect vulnerable immigrants, and with principles for mobilizing congregations for social change more effectively.