Sufism or taṣawwuf (Arabic: تصوّف‎) is defined by its adherents as the inner, mystical dimension of Islam. A practitioner of this tradition is generally known as a ṣūfī (صُوفِيّ).

Classical Sufi scholars have defined Sufism as "a science whose objective is the reparation of the heart and turning it away from all else but God". Alternatively, in the words of the Darqawi Sufi teacher Ahmad ibn Ajiba, "a science through which one can know how to travel into the presence of the Divine, purify one's inner self from filth, and beautify it with a variety of praiseworthy traits".

Classical Sufis were characterised by their attachment to dhikr (a practice of repeating the names of God) and asceticism. Sufism gained adherents among a number of Muslims as a reaction against the worldliness of the early Umayyad Caliphate (661-750 CE). Sufis have spanned several continents and cultures over a millennium, at first expressed through Arabic, then through Persian, Turkish and a dozen other languages. "Orders" (ṭuruq), which are either Sunnī or Shī'ī or mixed in doctrine, trace many of their original precepts from the Islamic Prophet Muhammad through his cousin 'Alī, with the notable exception of the Naqshbandi who trace their origins through the first Caliph, Abu Bakr. Other exclusive schools of Sufism describe themselves as distinctly Sufi. Modern Sufis often perform dhikr after the conclusion of prayers.

Hamza Yusuf Hanson is an American Islamic scholar, and (with Zaid Shakir and Hatem Bazian) is co-founder of Zaytuna College in Berkeley, California, United States. He is a convert to Islam, and is one of the signatories of A Common Word Between Us and You, an open letter by Islamic scholars to Christian leaders, calling for peace and understanding. He has described the 9/11 attacks as "an act of 'mass murder, pure and simple'". Condemning the attacks, he has also stated "Islam was hijacked ... on that plane as an innocent victim".The Guardian newspaper in the United Kingdom reported that he "is arguably the west's most influential Islamic scholar" and added that "many Muslims find his views hard to stomach."

Hamza Yusuf was born to two academics in Washington State and raised in Northern California. In 1977, he became Muslim and subsequently traveled to the Muslim world and studied for ten years in the United Arab Emirates, Saudi Arabia, as well as North and West Africa. Hamza Yusuf spent four years studying in the United Arab Emirates and elsewhere in the Middle East. Later he traveled to West Africa and studied in Mauritania, Medina, Algeria, and Morocco under such scholars as Murabit al Haaj; Baya bin Salik, head of the Islamic court in Al-'Ain, United Arab Emirates; Muhammad Shaybani, Mufti of Abu Dhabi; Hamad al-Wali; and Muhammad al-Fatrati of Al Azhar University in Cairo, Egypt.^{[citation needed]} After more than a decade abroad, he returned to the United States and earned degrees in nursing from Imperial Valley College and religious studies at San José State University.^{[citation needed]}