An affair. It can rob a couple of their relationship, their happiness, their very identity. Why do people cheat, even those in happy marriages? Why does an affair hurt so much? When we say infidelity, what exactly do we mean? Do our romantic expectations of marriage set us up for betrayal? Is there such a thing as an affair-proof marriage? Is it possible to love more than one person at once? Can an affair ever help a marriage? For the past ten years, couples' therapist Esther Perel has traveled the globe and worked with hundreds of clients who have grappled with infidelity. Betrayal hurts, she writes, but it can be healed. An affair can even be the doorway to a new marriage -- with the same person. With the right approach, couples can grow and learn from these tumultuous experiences, together or apart. Affairs, she argues, have a lot to teach us about modern relationships: what we expect, what we think we want, and what we feel entitled to. They offer a unique window into our personal and cultural attitudes about love, lust, and commitment. Through examining illicit love from multiple angles, Perel invites readers into an honest, enlightened, and entertaining exploration of modern marriage in its many variations.