Although it was not directly named in the U.S. Constitution, federalism is a central principle of U.S. government. It is important for students to learn about federalism to comprehend the U.S. federal system and recognize examples of federalism in other countries. Teaching and learning about federalism is essential to education for citizenship in a democracy. This digest: (1) defines federalism and discusses basic characteristics of the U.S. federal system; (2) provides an overview of the changing nature of federalism in the United States and internationally; (3) calls upon teachers to conduct deliberative discussions of federalism in relationship to other principles of constitutional democracy; and (4) recommends Internet resources related to federalism. (BT)