Is the human self singular and unified or essentially plural? This book explores the seemingly disparate ways that Christian theology and the secular human sciences have approached this complex question. Through an original analysis of recent theological and secular accounts of self and personhood, this book examines the extent of the intertheoretical disparity and its broader implications for theology's dialogue with the human sciences in general, and psychology in particular. It explains why theologians ought to take questions about the plurality of self very seriously, and how they overlap with many of the central concerns of contemporary theological anthropology, including the notions of relationality, particularity and human sinfulness. Introducing a novel psychological framework to distinguish various understandings of self-disunity, the author argues that contemporary theology's blanket condemnation of self-multiplicity is misconceived, and identifies a possible means of reconciling theological and human scientific accounts.