Tzahi Weiss. Sefer Yeṣirah and Its Contexts: Other Jewish Voices , Philadelphia, PA: University of Pennsylvania Press, 2018. Pp. ix, 196. $59.95. ISBN: 9780812249903. The Hebrew text known as the Sefer Yeṣirah , or Book of Formation , has piqued the interest of scholars of early medieval Jewish philosophy and those of central- to late-medieval Jewish mysticism and magic for centuries. In Sefer Yeṣirah and Its Contexts: Other Jewish Voices , Tzahi Weiss extends interest in this text to scholars of early medieval Jewish mysticism, magical praxis, and Jewish-Christian relations. Through an exploration of Sefer Yeṣirah ’s specific methods of letter speculation, grammar, and textual reception, Weiss presents a two-pronged argument. First, he contends that the much-debated compositional context of the Sefer Yeṣirah was most likely 7th-century Christian Syria. And, second, that early readers of the Sefer Yeṣirah understood it as a mystical and magical treatise long before the late 12th century, as is commonly assumed. Weiss divides his slim volume into an introduction, five chapters, an epilogue, and two appendices. The first appendix addresses scholarly arguments that the Sefer Yeṣirah originated in the Abbasid world and was influenced by Arabic grammar; the second appendix provides a Hebrew transcription of an 11th-century recension of the Sefer Yeṣirah (Ms. Vatican 299/4) that Weiss bases his arguments on, accompanied by Peter A. Hayman’s English translation. Along with a review of scholarship treating the text and a statement of Weiss’ departure from, indebtedness to, and contributions to the field, the Introduction provides a quick summary of the contents of the Sefer Yeṣirah as a treatise describing God’s formation of the world from numbers …