In a world where we have an endless number of options to swipe through, why do many of us repeatedly return to previous romantic partners? This book addresses this question by synthesizing the research on relationships that break up and renew (i.e. ‘on-again, off-again’ relationships) from various disciplines including communication, social psychology, family studies, and sociology. It explicates the various types and trajectories of on-again, off-again relationships, and uncovers how these relationships are different from those that do not split up and reconcile. Because on-again, off-again relationships challenge traditional notions of relationship stability and highlight the fluctuating nature of relationships, alternative conceptualizations of stability are also reviewed. This book is a theoretical and practical resource for researchers, students, and professionals interested in understanding why partners repeatedly reconcile with ex-partners.