Christianity, Judaism, and Islam are often treated as autonomous, stable and independent of each other. In fact, across the long course of their histories, the three religions have developed in interaction with, and thinking about, each other. This book shows how, from their beginnings to the present day, the three religions were and continue to be “co-produced,” shaping and reshaping themselves through processes of simultaneous identification and dis-identification with their rival “siblings”/neighbors. It uncovers a world in which the three religions are interdependent, constantly transformed by a fundamentally ambivalent form of “neighborliness.” Beginning with the emergence of this neighborliness in the scriptures of the three religions and ending in the present day, the book traces the constant transformation of religious communities through this co-production, at times purely in the cultural imagination. The vast majority of medieval Christians, for example, never met a living Muslim or Jew, but they thought about them a great deal. In certain times and places (e.g., medieval Spain), Muslims, Jews, and Christians did live in close proximity, and this book shows how these neighbors loved, tolerated, massacred, expelled, and thought about each other—all in the name of God. No matter how wrong-headed or bizarre these ways of a distant past may seem, they have something to teach us about how we think and act today. Teach, not by way of example, whether positive or negative, but as a stimulus to critical awareness about the workings of our own assumptions, hopes, and habits of thought.