In Revoking Citizenship, Ben Herzog, a lecturer at the Ben-Gurion Research Institute in Israel, traces the evolution of expatriation in the United States as well as the rationales for revoking citizenship. Using specific examples, he demonstrates that over the decades rationales for expatriation have moved from assumptions about the inevitability of a citizen's loyalty to a single state to today's acceptance of dual citizenship in an increasingly globalized world. In telling this history, Herzog explores the role of revocation as the vehicle for and understanding of citizenship shifts. His book reveals how fragile the concept of citizenship in the United States has been, especially at times-such as war-when the sovereignty of the nation is threatened. His exploration of post-citizenship scrutiny of the polity's members reminds us that the concept of citizenship is not nearly as static as we might believe. Herzog's thesis is that, contrary to the vision of citizenship as immutable in a democracy, rights to citizenship occur within political and sociological contexts that determine how a member of the polity maintains membership. Herzog mines congressional debates, State Department correspondence, treaties, and U.S. Supreme Court opinions to show how citizenship-and the state's right to revoke it-has been determined over time. The book explores the notion of revoking citizenship from the perspective of the decision makers involved-Congress, the executive branch, and the courts. Herzog then analyzes the discourse around revocation of citizenship today through the lens of the war on terror. He concludes with an analysis of dual citizenship and the ways the narrative has now shifted to exploring the motivations of dual citizens to determine whether revocation of citizenship is ever appropriate. Herzog argues, ultimately, that the United States has operated under an unexamined assumption that sovereign entities can and do exercise the right to revoke citizenship, just as they have the ability to determine citizenship. For example, at the turn of the 20th century Congress passed the 1907 Expatriation Act, which set out conditions for loss of citizenship, as well as conditions for overcoming the presumption of expatriation. One such condition for citizenship loss was enrolling in military service in a nation that required an oath of loyalty. The presumption during this period was that a citizen could be loyal to only one country at a time. Other times-as is more recently the case-revocation is done despite the state's acceptance of dual-citizenship status. This has been true since the Supreme Court held that congressional efforts to unilaterally revoke citizenship as a punishment violated the Eighth Amendment in Trop v. Dulles (356 U.S. 86 (1958)). Today, lawfully obtained citizenship can be revoked only upon a showing that the citizen actively seeks expatriation. (See 8 U.S.C. §§ 1481, 1488.) The statute notes that one loses nationality by "voluntarily performing" certain acts "with the intention of relinquishing" nationality. (8 U.S.C. § 1481). Such acts include taking an oath of allegiance to or serving in the armed forces of a foreign state, serving as a public official or accepting employment with the government of a foreign state, making formal renunciation of nationality at a consulate in a foreign state, or committing an act of treason. In each of these cases, the debates center on whether a citizen has voluntarily expressed intent by his or her words or conduct. Interestingly, as Herzog points out, the United States' exercise of citizenship revocation is most robust when the country and its government invoke sovereignty principles. Principal among these is the right to expel those who fail to pass loyalty tests at times when the government considers itself in a war against foreigners. But the racialized application of such citizenship-revocation efforts is striking. The federal government has invoked its sovereign rights to revoke U.S. citizenship for those of Chinese descent at the turn of the 20th century; of Japanese descent during World War II; and today for those of Middle Eastern descent whom it considers terrorists. While Herzog does a fine job of describing these examples, I wish he had mined the racialized nature of these historical moves more deeply. Herzog's contribution to the growing debate over membership in our polity is important for its reminder that citizenship has historically been contingent in the United States, despite the claims to constitutional status that citizenship might invoke. At 139 pages (not including notes), it is a short read that will induce the reader to rethink the nature of citizenship in our democracy. Leticia Saucedo is a law professor at UC Davis, where she teaches employment, labor, and immigration law.