The Strategic Use of Fidelity in Romantic Relationships interrogates the monogamy myth by identifying the logical and pragmatic fissures in monogamy theory and practice. Beggan’s expansive examination begins with a simple observation regarding divorce rates and proceeds to address previous research, popular defenses, and persistent assumptions regarding Western culture’s continued valorization of monogamy particularly in its most common form, marriage. Beggan’s provocative concept of “defensive monogamy” challenges existing conceptualizations and data regarding fidelity and is a significant contribution to relationship studies. Through “defensive monogamy,” he more accurately and more rationally describes the way in which relationships function and the ways they dysfunction. In the words of J. P. Morgan, people make decisions for two reasons: the “good reason” and “the real reason.” Beggan’s excellent work investigates the real reasons we deploy monogamy and how those reasons frequently derail the fidelity and security couples seek.