The Tibetan Buddhist Schools
Please check the following categories for more information.

Gelugpa
"School of the virtuous"
Founded by Tsongkhapa.
The teaching emphasis on the observation of monastic rules (Vinaya-pitaka) and thorough study of authoritative texts, principal among these is the literature on the stages of the path (lam-rim) and the systematic works on the various Buddhist doctrinal views (Siddhanta).

Kadampa
"Oral instruction"
Founded by Atisha in the 10th century.
The most important teaching of the Kadampas became known by the name Lo-Jong("training the mind"). This school did not survive as an independent tradition in Tibet. A newly formed Kadampa tradition has been expanding in the West after 1970.

Kagyupa
"Oral transmission lineage"
The teaching were brought to Tibet from India in the 11th century by Marpa. The central teaching is the "great seal" (mahamudra) and the six dharmas of Naropa.

Nyingmapa
"school of the Ancients"
The oldest Buddhist traditions of Tibet.
The teaching were brought to Tibet from India in the 8th century by Padmasambhava, Vimalamitra, and Vairochana.
The central teaching is "dzochen". The systematization of the dzochen teaching by Lonchenpa and his commentary on it are considered authoritative.

Sakapa
This school named after the Sakya ("Gray Earth") monastery, located in southern Tibet. The monastery were founded in the year 1073, its abbots devoted themselves primarily to the transmission of a cycle of Vajrayana teaching known by the name of "path and goal"(Lamdre).
The central teaching is to create a systematic order for the Tantric writing (Tantra) as well the problem of Buddhist logic.