Because of the financial and social hardship faced after divorce, most people assume that generally husbands have instigated divorce since the introduction of no-fault divorce. Yet women file for divorce and are often the instigators of separation, despite a deep attachment to their children and the evidence that many divorces harm children. Furthermore, divorced women in large numbers reveal that they are happier than they were while married. They report relief and certainty that they were right in leaving their marriages. This fundamental puzzle suggests that the incentives to divorce require a reexamination, and that the forces affecting the net benefits from marriage may be quite complicated, and perhaps asymmetric between men and women. This paper considers women's filing as rational behavior, based on spouses' relative power in the marriage, their opportunities following divorce, and their anticipation of custody.