We discuss the extraordinary reception-history of the extraordinary text known as Sefer Yetsirah, the ‘Book of Formation‘. The Sefer Yetsirah would eventually become a foundational text for the Kabbalist movements of the high middle ages, but it was (and is) much more than that. Professor Langermann lays out the evolutions in reading this text from Sa‘adia Gaon to Aryeh Kaplan.