He was educated in Medina (Saudi Arabia), and travelled in Iraq and later, Iran. It was in Iran that he began preaching against the Sufi Muslims then predominant in the region. After his return to Medina he wrote his Kitab at-tawhid (Arabic, "Book of Unity"), which became the main text for the Wahhabi sect of Islam. His teachings led to a controversy which resulted in him being expelled; he moved onto the city of Ad-Dir'iyah (Saudi Arabia).
Wahhabism spread due to an alliance Abd al-Wahhab and Ibn Sa'ud; they initiated a campaign of conquest that has still is in existence to this day.
Followers of his doctrine usually call themselves Muwahhidun ("Unitarians"); Non-Muslims refer to followers of his sect as Wahhabists.
Abd al-Wahhab's theological program aimed to cleanse Islam of what he viewed as bidah (innovations), deviances, heresies and idolatries. In his view, by following his theology and practice, a Muslim would return to the original form of Islamic faith that Allah originally had intended all of mankind to follow. Most historians (both Arab and non-Arab), however, hold that Wahhabism is in fact a new form of Islam, containing many changes in both theology and practice. Wahhabi himself though advocated the Hanbali school of Islamic jurisprudence (fiqh), since it is the most traditional and opposed to innovation.
His particular interpretation of Islam forbids the use of gravestones as tending toward idolatry and it tries to avoid any practices that did not exist at the time of Muhammad. Wahhabism is the official practice of Islam in Saudi Arabia; Saudi Arabia considers it a state crime to convert to any other form of Islam, or to convert to any other religion.