The Longchen Nyingthik (Tib. “Heart Essence of the Vast Expanse) is a Terma cycle revealed by the master Jigme Lingpa. Since its inception in the late 18th century, it has become one of the most widespread sets of teachings in the Nyingmapa tradition. It is particularly known and loved for its extensive commentarial literature, which includes practice manuals such as the famed Words of my Perfect Teacher.
These teachings were originally transmitted by the master Padmasambhava to King Trisong Deutsen, the Dakini Yeshe Tsogyal and the Lotsawa Vairochana at Samye Monastery in central Tibet. As the time for these teachings to spread was not yet right, they were then written in symbolic script by Yeshe Tsogyal, entrusted to the Dakinis, and hidden to be revealed at a later time. The king later reincarnated as the Treasure Revealer Jigme Lingpa, who recalled the teachings he had received and, recognizing the time was ripe for them to be practiced, put them down in writing and began to teach.
Jigme Lingpa, the Terton who revealed the Longchen Nyingthik cycle of teachings, was as stated above, a reincarnation of two important masters, Vimalamitra and King Trisong Deutsen. As the embodiment of these two figures, Tibet's two primary Dzogchen lineages were combined in Jigme Lingpa -- the Vima Nyingthik and Khandro Nyingthik, both of which are contained in the Nyingthik Yabshi. Hence, the Longchen Nyingthik terma cycle is considered a condensation of these profound teachings.
The texts that were revealed by Jigme Lingpa, in their present-day form, comprise three volumes, known as the Nyingthik Tsapod, (Wylie: snying thig rtsa pod) which is made up of numerous treatises, sadhanas and prayers. Its contenents deal primarily with tantric practice, in particular Development Stage and Dzogchen.