The Tibetan practice of bcud len, or 'extracting the essence', has been for long a neglected aspect of Tibetan medical and spiritual knowledge with scattered evidence and little certainty regarding its origins or the extent of its effective presence, either in the past or at currently. In this study, seventy-three texts have been identified and tabulated. Of these, sixty-seven have been summarised and commented on, and five of these, each representative of one type of the practice, have been translated in full. All but a handful of these texts have not been translated previously. The research findings suggest that, whatever its influences from Indian, Chinese or other medical cultures, bcud len soon evolved into a distinctively Tibetan method of life enhancement, with teachings that emphasise both spiritual and medical aims and the use of indigenous Tibetan remedies, accompanied in some cases by particular rituals. The content of the texts indicates that the term bcud len can be applied legitimately to practices involving ritually empowered pills and elixirs which are ingested, respiratory and yogic exercises, dietary restrictions and rituals involving mantra recitation, visualisation and yab yum union with a consort, in that all these are considered to be means of obtaining 'the essence'. The teachings offer extensive material for those interested in the evolution and contemporary practice of Tibetan medicine, especially its botanical aspects, and for historians of ritual. In particular, the texts provide ample evidence of the lineage tradition in Tibetan religious culture, citing examples of transmissions through gter ma, whereby teachings are preserved in secret to be recovered at a future date by a gter ton or treasure revealer. The final section contains conversations with Tibetan doctors, lamas and contemporary practitioners of bcud len in Asia and the West that complement recent ethnographic studies in the field testifying to the continuing vitality of the tradition.