The Lineage of Immortals (Sanskrit Amaraugha) is the earliest account of a fourfold system of yoga in which a physical practice called Haṭha is taught as the means to a deep state of meditation known as Rajayoga. The Amaraugha was composed in Sanskrit during the twelfth century and attributed to the author Goraksanatha. The physical yoga practices have a pre-history in a tantric Buddhist milieu but were here adapted for a Saiva audience. The treatise explains how Saiva yogis move kundaalini,  unite Sakti with Siva, and achieve Rajayoga. Three hundred years later, the author of the Haṭhapradipika incorporated almost  all the Amaraugha's verses on Haṭhayoga into his own work, which became a definitive exposition of physical yoga. The study of the Amaraugha reveals not only the genesis of Haṭha and Rajayoga but also the creation of the most influential model of Hathayoga in the early modern period. This book presents the first critical edition and annotated translation of the Amaraugha, as well as a later recension, called the Amaraughaprabodha, with an introduction that explores the profound significance of both works for the history of yoga.