Wahhabism (Arabic: ٱلْوَهَّابِيَةُ, romanized: al-Wahhābiyya) is a Sunni Islamic fundamentalist movement originating in Najd, Arabia. Founded eponymously by Arabian scholar Muhammad ibn Abd al-Wahhab (c. 1703–1792), Wahhabism is followed primarily in Saudi Arabia and Qatar.

The reform movement was established in central Arabia and later in South Western Arabia. It opposed rituals related to the veneration of Muslim saints and pilgrimages to their tombs and shrines, which were widespread amongst the people of Najd. Ibn Abd al-Wahhab and his followers were highly inspired by the influential thirteenth-century Hanbali scholar Ibn Taymiyyah (1263–1328 C.E/ 661 – 728 A.H) who called for a return to the purity of the first three generations (Salaf) to rid Muslims of inauthentic outgrowths (bidʻah), and regarded his works as core scholarly references in theology. While being influenced by their Hanbali doctrines, the movement repudiated Taqlid to legal authorities, including oft-cited scholars such as Ibn Taymiyya and Ibn Qayyim (d. 1350 C.E/ 751 A.H).

Wahhabism has been variously described as "orthodox", "puritan(ical)", "revolutionary", and as an Islamic "reform movement" to restore "pure monotheistic worship" by devotees. The term "Wahhabism" was not used by Ibn 'Abd al-Wahhab himself, but is chiefly used by outsiders, while adherents typically reject its use, preferring to be called "Salafi" (a term also used by followers of other Islamic reform movements as well). The movement's early followers referred to themselves as Muwahhidun (Arabic: الموحدون, lit. '"one who professes God's oneness" or "Unitarians"') derived from the term Tawhid (the oneness of God). The term "Wahhabism" is also used as a sectarian and Islamophobic slur. Socio-politically, the movement represented the first major Arab-led protest against the Turkish, Persian and foreign empires that dominated the Islamic World since the Mongol invasions and the fall of Abbasid Caliphate in the 13th century; and would later serve as a revolutionary impetus for 19th-century pan-Arabism.

In 1744, Ibn ʿAbd al-Wahhab formed a pact with a local leader, Muhammad bin Saud, a politico-religious alliance that continued for the next 150 years, culminating politically with the proclamation of the Kingdom of Saudi Arabia in 1932. His movement would eventually arise as one of the most influenctial 18th century anti-colonial reform trends that spread across the Islamic World; advocating a return to pristine Islamic values based on Qur’an and Sunnah for re-generating the social and political prowess of Muslims; and its revolutionary themes influenced numerous Islamic revivalists, scholars, pan-Islamist ideologues and anti-colonial activists as far as West Africa. For more than two centuries through to the present, Ibn ʿAbd al-Wahhab's teachings were championed as the official form of Islam and the dominant creed in three Saudi States. As of 2017, changes to Saudi religious policy by Crown Prince Mohammed bin Salman have led to widespread crackdown on Islamists in Saudi Arabia and rest of the Arab World. In 2018 Saudi Crown Prince Mohammed bin Salman, denied that anyone "can define this Wahhabism" or even that it exists. By 2021, the waning power of the religious clerics brought forth by the social, religious, economic, political changes and a new educational policy asserting a "Saudi national identity" that emphasize non-Islamic components have led to what has been described as the "post-Wahhabi era" of Saudi Arabia.

The decision to celebrate the "Saudi Founding Day", annually on 22 February since 2022, to commemorate the 1727 establishment of Emirate of Dir'iyah by Muhammad ibn Saud; rather than the past historical convention that traced the beginning to the 1744 pact of Ibn 'Abd al-Wahhab; have led to the official "uncoupling" of the religious clergy by the Saudi state.