Book excerpt: Analyses of 150 cases of espionage against the United States by American citizens between 1947 and 2001. Provides detailed data on the demographic and employment characteristics of American spies, on the means and methods they used to commit espionage, on their motivations, and on the consequences they suffered. Collected materials on the cases supplement the analyses conducted with a database that allows comparison of groups and the identification of trends. Factors highlighted include changes in espionage by Americans since the end of the Cold War and the impact of globalization and networked information systems on the practice of espionage.