Traditionally within Tibet there are many groupings of schools, such as the Eight Chariots of the Practice Lineage. However, the most well-known grouping in modern times is into the four major schools: Nyingma, Sakya, Kagyu and Gelugpa.
The Sakya, Kagyu and Gelugpa are "new schools," established during the second wave of Buddhism's transmission from India to Tibet in the 11th and 12th centuries.
In general, the lineage traditions are supported by different, independent Tibetan institutions. Each of these major schools were predominant in Tibet during different periods of Tibetan history, and each have geographical areas where they are more popular. There are also innumerable subschools and divisions within each of these four major schools, a tendency which is heightened by the individual nature of lineage transmission. Still, many unifying movements have informed Tibetan institutions over the centuries. In particular, in the Nineteenth Century, the Rime movement led by Jamgon Kongtrul the Great and the great Jamyang Khyentse, revitalized many Sakya, Nyingma and Kagyu institutions by promoting respect and knowledge by each of the other.