ROY ROSENZWEIG is professor of history and Director of the Center for History and New Media at George Mason University. He is the author of several books including The Park and the People: A History of Central Park(with Elizabeth Blackmar). He is also the coauthor of Who Built America?, a two-volume multimedia CD-ROM.DAVID THELEN is professor of history at Indiana University and editor of the Journal of American History. He is also the editor of Discovering America: Essays on the Search for an Identity, and the author of several books including Becoming Citizens in the Age of Television.