The Khecharividya of Adinatha, a Sanskrit text dated to pre-1400 ce, teaches khechari-mudra, one of the most important exercises of hatha-yoga, in which the tongue is inserted above the palate in order to drink the amrita or nectar of immortality dripping from the top of the skull. It is said to bestow immortality, the ability to remain in deep meditation for long periods and the power of flight upon its practitioners. The text has been edited for the first time and has never before been accessible to an English-speaking readership. It is accompanied by an introduction and an extensively annotated translation. The author has drawn on twenty-seven Sanskrit manuscripts and original fieldwork amongst yogins in India to demonstrate how earlier tantric yogic techniques developed and mutated into the practices of hatha-yoga. The work sheds new light on the development of hatha-yoga and explains its practices.