This paper examines the U.S. social insurance system, which we define broadly to include both programs supported by dedicated taxes and other federal programs that provide income support, assistance in meeting basic needs, or services to improve economic opportunity. The paper considers the social insurance system as a whole as well as its component parts, providing an overview of major federal programs in the areas of education and workforce development, health, income support, nutrition, and housing. The paper covers how the social insurance system is organized, how eligibility is determined and who benefits, how the benefits and services are delivered, and how the system affects poverty and inequality. We focus primarily on the system as it operated prior to the onset of the COVID-19 pandemic, but also look at how various programs respond to economic downturns. Coming at a time when policymakers will start shifting their focus from using the social insurance system to provide relief from the pandemic and recession to considering what changes should be made in the system on an ongoing basis, the paper also reprises an array of proposals to strengthen the system in various ways that The Hamilton Project has commissioned in recent years.