"Sufism (Arabic: ٱلصُّوفِيَّة), also known as Tasawwuf[1] (Arabic: ٱلتَّصَوُّف), is mysticism in Islam, "characterized ... [by particular] values, ritual practices, doctrines and institutions". It is variously defined as "Islamic mysticism", "the inward dimension of Islam" or "the phenomenon of mysticism within Islam". Sufism began very early in Islamic history and represents "the main manifestation and the most important and central crystallization of" mystical practice in Islam. Practitioners of Sufism have been referred to as "Sufis" (from صُوفِيّ, ṣūfīy).
Historically, Sufis have often belonged to different ṭuruq or "orders" – congregations formed around a grand master referred to as a wali who traces a direct chain of successive teachers back to the Islamic prophet Muhammad. These orders meet for spiritual sessions (majalis) in meeting places known as zawiyas, khanqahs or tekke. They strive for ihsan (perfection of worship), as detailed in a hadith: "Ihsan is to worship Allah as if you see Him; if you can't see Him, surely He sees you." Sufis regard Muhammad as al-Insān al-Kāmil, the complete human who personifies the attributes of Absolute Reality, and view him as their ultimate spiritual guide.
Sufi orders (tariqa) trace most of their original precepts from Muhammad through Ali ibn Abi Talib, with the notable exception of the Naqshbandi order, who trace their original precepts to Muhammad through Abu Bakr.
Although the overwhelming majority of Sufis, both pre-modern and modern, were and are adherents of Sunni Islam, there also developed certain strands of Sufi practice within the ambit of Shia Islam during the late medieval period, particularly after the Safavid conversion of Iran from majority Sunni to Shia. Traditional Sufi orders during the first five centuries of Islam were all based in Sunni Islam. Although Sufis were opposed to dry legalism, they strictly observed Islamic law and belonged to various schools of Islamic jurisprudence and theology.
Sufis have been characterized by their asceticism, especially by their attachment to dhikr, the practice of remembrance of God, often performed after prayers. They gained adherents among a number of Muslims as a reaction against the worldliness of the early Umayyad Caliphate (661–750) and have spanned several continents and cultures over a millennium, initially expressing their beliefs in Arabic and later expanding into Persian, Turkish, Punjabi and Urdu, among others. Sufis played an important role in the formation of Muslim societies through their missionary and educational activities. According to William Chittick, "In a broad sense, Sufism can be described as the interiorization, and intensification of Islamic faith and practice."
Despite a relative decline of Sufi orders in the modern era and criticism of some aspects of Sufism by modernist thinkers and conservative Salafists, Sufism has continued to play an important role in the Islamic world, and has also influenced various forms of spirituality in the West."
(from Wikipedia)
Sufism in the West (by Malik, et al.)