Longde (Wylie: kLong-sde; Sanskrit: Abhyantaravarga) is the name of one of three scriptural divisions within Atiyoga, also known as Dzogchen
(Wylie: rDzogs-chen) or the Great Perfection which is itself the pinnacle of the ninefold division of practice according to the Nyingma school of Tibetan Buddhism.
The name Longde is translated as 'Space Division' or 'Space Series' of Dzogchen and emphasises the emptiness (strong-pa) or spaciousness (klong) aspect of the Natural State.
Penor Rinpoche states that due to the different approaches of various Dzogchen lineages, three sub-schools have developed of which longde is one.
The other two divisions or schools are Semde (Mind Series) and Menngagde (Oral Instruction Series).
Penor Rinpoche refers to Longde as the Centredness School and is attributed to Longde Dorje Zampa, Shrisimha and Vairotsana's lineage.
These three divisions were introduced by the Buddhist scholar Manjushrimitra.
As Great Perfection texts, the texts of all three divisions are concerned with the basic primordial state;
the nature of mind-itself (which is contrasted with normal conscious mind).
They are related to the 'Three Statements' (Tshig-gsum gnad-brdeg) of Garab Dorje (Wylie: dGa'-rab rdo-rje).
It is important to note that the three series do not represent different schools of Dzogchen practice as much as different approaches to the same goal, that being the basic, natural, and primordial state.
As is common throughout much Buddhist literature, Tibetan Buddhism in particular, gradations in the faculties of practitioners are also ascribed to the three divisions, they being seen as appropriate for practitioners of low, middling, and high faculties, respectively.
The Space Division is related to Garab Dorje's second statement, removing doubts.
It teaches methods of meditation that enable the practitioner to get beyond any doubts he or she may have concerning the natural state.
"Samantabhadra’s Royal Tantra of All-Inclusive Vastness" (Sanskrit: Maha-avarnta-prasarani-raja-tantra-nama; Tib. Wylie: klongchen rab byams rgyal po’i rgyud ces bya ba bzhugs so) is renowned as the “king of tantras belonging of the Space Section.
Guarisco & McLeod 2005: p. 520) list the tantric texts belonging to the Space Division thus:
According to Thondup & Talbott (1997: p. 48) there are only seven extant texts of the Space Class and they are collected in the Nyingma Gyubum.