The Nyingma Tradition prior to the 17th century was a large but loose grouping of independent family lineages with some small monasteries and hermitages. After the 17th century large monastic institutions were created with a number of them funded and supported by the 5th Dalai Lama. The Nyingma Tradition is doctrinally closest with the various Marpa/Dagpo Kagyu Traditions.
"The Nyingma Tradition, the old Secret Tantra, classifies the Buddha's Dharma into nine successive Vehicles, collectively contained in the Cause Vehicle and the Result Vehicle of Tantra. The Cause Vehicle has three divisions: the Hinayana Vehicle of the Sravakas, the Hinayana Vehicle of Pratyekabuddhas and the Mahayana Vehicle of the Bodhisattvas. In the Result Vehicle of Tantra there are two divisions: the three Outer Tantric Vehicles, and the three great methods of the Inner Tantric Class. All these have a great many definitions and explanations concerning their view, meditation, action and result, but it is not possible to write these explanations here.
There are three lineages in the old translations of the Nyingma Tantras: the 'Distant Oral Lineage' (Tibetan: Ring.rGyud.bKah.ma - from the direct oral teachings of the Buddha); the 'Near Treasure Lineage' (Tib: Nye.rGud.gTer.ma - from teachings of discovered treasure texts, written and concealed in holy places by Guru Rinpoche, Khandro Yeshe Tsogyal and others; for the benefit of future generations), and the 'Lineage of Profound Pure Visions' (Tib: Zab.mo.dag.sNang - from teachings received by various Saints during visions in meditation and post-meditation)."