This entry addresses unemployment insurance as the cornerstone of the Social Security Act of 1935 and, accordingly, as a cornerstone of the modern U.S. social welfare system. After providing a brief historical background of the Unemployment Insurance program, including key ties to the social work profession, this entry provides information about underlying ideological perspectives, and about program design and implementation. Key considerations are discussed with regard to the impact of the economic downturn and the global COVID-19 pandemic on unemployment insurance using a Keynesian framework. Finally, a discussion is offered pertaining to the legacy and possible reform of the Unemployment Insurance program.