An affair: it can rob a couple of their relationship, their happiness, their very identity. And yet, this extremely common human experience is so poorly understood. What are we to make of this time-honored taboo - universally forbidden yet universally practiced? 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 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? Perel weaves real-life case stories with incisive psychological and cultural analysis in this fast-paced and compelling book.