This book began as an expert opinion prepared for the attorney general of Canada. A group of Fundamentalist Mormons in the town of Bountiful, British Columbia, had challenged the constitutionality of Canada's traditional criminal prohibition on polygamy. The attorney general sought to uphold the law. Various religious liberty and human rights groups wanted it struck down. My task was to document the Western legal tradition's arguments in favor of monogamy and against polygamy, from classical and biblical times until today.

It was not an easy task, in part because I am a strong advocate of human rights and usually counsel the protection of religious freedom, even for religious communities that depart from the cultural mainstream. It was also not an easy task because the Western legal tradition has not been clear or consistent in its arguments against polygamy, despite making polygamy a serious crime since the third century. My task for the attorney general was to sketch some of these shifting teachings of the tradition and report on them. The challenge in writing this book was to fill in and filigree the historical picture only crudely sketched in my opinion. Much of this book takes up that task, filling an ample and surprising gap in the historical literature (at least in a Romance language). The further challenge was to determine whether the various traditional Western arguments for monogamy and against polygamy, once fully retrieved and reconstructed, are still cogent in our day. I believe they are, and the last part of this book presses that case, albeit more briefly as it is the historical arguments against polygamy, not the modern policy implications of this history, that are my main concern.

I have incurred a number of debts in preparing this volume. I wish to thank the crack legal team in the attorney general of Canada office in Vancouver – Craig Cameron, Keith Reimer, and B.J. Wray – for many stimulating conversations about this topic.