This entry examines why our nation’s Social Security system was built, what it does, and what must be done to maintain and improve this foundational system for current and future generations. After a discussion of the social insurance approach to economic security and its underlying principles and values, the evolution of America’s Social Security system is reviewed—beginning with the enactment of the Social Security Act of 1935, through its incremental development, to the changed politics of Social Security since the mid-1990s. Next, program benefits and financing are described and contemporary challenges and related policy options are identified, in terms of both the program’s projected shortfall and the public’s need for expanded retirement, disability, and survivorship protections. The entry concludes by noting that social workers have an important role to play in shaping Social Security’s future.