Traditionalism is a Sufi/Islam-inspired [but not orthodox Sufism or Islam, despite claims to the contrary - see Sedgwick 1999 Traditionalist Sufism ] neo-esotericist movement that was founded by the French scholar Rene Guenon (1886-1951). The term "Tradition" refers to the central idea that the great Faiths all derive from a single Primordial Tradition, which itself is directly inspired as on-going Revelation from the Transcendental source. This is in keeping with the Islamic belief that "God has sent a prophet (or Messenger) to every people" All the Great Religions and are therefore merely different expressions of the same Divine Logos, and hence are all equally valid spiritual paths to Salvation. Traditionalism therefore is concerned with the abiding inner or esoteric Truth or Principle that it understands to be at the heart of the various exoteric religious Traditions.
Other Traditionalists include Guenon's student Frithjof Schuon, Titus Burkhardt, Martin Lings, art historian and philosopher Ananda K Coomaraswamy, Seyyed Hossein Nasr, the Egyptologist R.A. Schwaller deLubicz, and a number of others. Thinkers sympathetic to the Traditionalist view include mythographer Joseph Campbell and Mircea Eliade, scholar of comparative religions Huston Smith, Indianologist Alain Danielou, E.F. Schumacher, and Prince Charles.
Guénon had a low opinion of modernity which he believed had degenerated from or corrupted the Divine Revelation and authentic spiritual civilization, and other Traditionalists and Traditionalist-supporters tend to share this view.
Traditionalist anti-modernity means the rejection of anything to do with the modern and postmodern West, including, all elements of science that conflict with traditional accounts of the universe. One thus finds Traditionalists like the Islamic scholar Seyyed Hossein Nasr advocating a Creationist viewpoint, because secular evolutionary science is seen to be at variance with the truths of traditional cosmologies. Dr. Seyyed Hossein Nasr goes so far as to flatly deny the possibility of reconciliation between science and religion. See also Kenneth Oldmeadow's essay The Firmament Sheweth His Handiwork - Re-awakening a Religious Sense of the Natural Order.
There is an occasional tendency among some "fringe" Traditionalists to be affiliated with the Right. Guenon's friend the fascist philosopher Julius Evola is often included among the Traditionalists, although Guenon never held fascistic or antisemitic views. The Russian scholar and political activist Alexander Dugin (b. 1962) is founder of the contemporary Russian school of geopolitics known as Eurasianism or Neo-Eurasianism, a Putin supporter and the former ideological guru for Edward Limonov's National-Bolshevik Party, although his fascist credentials seenm to have been exaggerated by the West. There may be a psychological equivalence here - people who want certainty (and hence hate modernity) are also likely to be attracted to strong religious positions (e.g. in the West religious funddamentalists are often (but not always!) to the right of the political spectrum. However, Traditionalism as a whole is in no way fascistic, and one can hardly blame the movement as a whole for the occaisonal malcontent.
Tradition - short good intro and excellent list of links
Traditionalist Sufism by Mark Sedgwick
This article was published in ARIES 22 (1999), pp. 3-24. It takes a very authoritative look at the somewhat uneasy relationships between orthodox Sufism and Islam on the one hand, and the Traditionialist Sufism of Guenon and Schuon on the other. Highly recommended reading for anyone who wuld like to know more about the roots of the modern Traditionalist movement.
Religio Perennis: Traditionalism, the Perennial Philosophy, and and Islamic Studies - book review that gives a good overview
Why I Am Not a Traditionalist