Towards the end of the 12th century, a small treatise titled Bahir (Light) appeared in southern France. This treatise, the first document of Kabbalah, proclaimed with a resounding impact an astonishingly new perspective on divinity: God's essence consists not only of ten powers, but one of these powers is distinctly feminine. Peter Schäfer initially traces the background of this idea from the biblical tradition of wisdom to the Middle Ages and then specifically investigates the reasons why it reached its first peak precisely in medieval France. The surprising answer: Judaism and Christianity rediscovered the femininity of God almost simultaneously in the 12th century—Christianity through an explosively growing veneration of Mary and Judaism through the emphasis on a feminine incarnation of God who descends to Earth and acts as a mediator between God and His creations. In contrast to the prevailing trend in research that seeks the roots of the feminine dimension of God in late antique Gnosticism, the book presents a model of fruitful interreligious exchange between Judaism and Christianity, beyond the common clichés of an eternal history of persecution and suffering. Drawing from shared sources, Judaism and Christianity did not constantly drift further apart, but rather pursued new and bold ideas that were common to both religions.