The Dzogchen teachings are traditionally classified into three divisions (sde gsum):

Tibetan Transliteration English Essence
སེམས་སྡེ་ Semde Mind Series Emphasizes direct introduction to the nature of mind through pointing-out instructions (ngo sprod).
ཀློང་སྡེ་ Longde Space Series Reveals the vast and open dimension of awareness — the primordial expanse (dbyings) free from limits.
མན་ངག་སྡེ་ Menngagde Instruction Series Contains the essential pith instructions (upadesha) for direct realization and the practice of thögal and rushen.

These teachings are transmitted through an unbroken lineage of realized masters (brgyud pa) from Samantabhadra, the primordial Buddha, to the present day.