This document provides an overview of the US system of federalism. It outlines the three branches of government and their roles, as well as key powers and limitations of federal and state governments. It also summarizes the evolution of federalism over time from a dual "layer cake" model to a more cooperative "marble cake" approach, and discusses factors that have shifted power between the national and subnational levels such as the expansion of federal power during the New Deal and Great Society eras versus the devolution of power during Reagan's presidency.