Latin American theology has evolved considerably during the past 40 years to encompass the mission of social justice. Formerly an instrument of social and economic oppression, the Catholic Church evolved during the decade of the 1960s to incorporate a grassroots perspective on the needs of the poor, the necessity of fundamental economic reform, and theological commitment to reforming the Church to meet the needs of Latin America’s most vulnerable. This line of thought has had a profound effect upon the work of priest and lay persons in the US-Mexico border region and has been an increasingly mainstream position of many Mexican and American bishops throughout the area. The theology of liberation calls for an active praxis of engagement in social reform rather than a passive acceptance of elite rule. This chapter describes the evolution of the perspective and its effect on social action in the border region.