This book takes a fresh look at John Milton’s major poems Paradise Lost, Samson Agonistes, and Paradise Regained and a few of the minor ones in light of a new analysis of Milton’s famous tracts on divorce. Luxon contends that Milton’s work is best understood as part of a major cultural project in which Milton assumed a leading role the redefinition of Protestant marriage as a heteroerotic version of classical friendship, originally a homoerotic cultural practice. Schooled in the humanist notion that man was created as a godlike being, Milton also believed that what marked man as different from God is loneliness. Milton’s reading of Genesis it is not good for man to be alone prescribes a wife as the remedy for this single imperfection, but Milton thought marriage had fallen to such a degraded state that it required a reformation. As a humanist, Milton looked to classical culture, especially to Plato, Aristotle, and Cicero, for a more dignified model of human relations friendship. Milton reimagined marriage as a classical friendship, without explicitly conceptualizing the issues of gender construction. Nor did he allow the chief tenet of classical friendship, equality, to claim a place in reformed marriage. Single Imperfection traces the path of friendship theory through Milton’s epistolary friendship with Charles Diodati, his elegies, divorce pamphlets, and major poems. The book will prompt even more reinterpretations of Milton’s poetry in an age that is anxiously redefining marriage once again.