Wahhabism is a socially conservative branch of Sunni Islam, founded in the 18th century by Muhammad ibn Abd al-Wahhab. In 1744, Wahhab made a critical alliance with Muhammad ibn Saud, the founder of the House of Saud, which is the royal house of modern Saudi Arabia.
While Wahhabism regards some of the more strict Salafist interpretations of Sunni Islam, such as that of Sayyid Qutb, as heresy, it is very socially conservative. It does not demand a return to the customs of the Prophet, but demands Islamist rule under sharia.
The Deoband school of Islam, formed in India and continuing in Pakistan, is a variant of Wahhabism, which used strict Islam to protest British colonial rule. Taliban theology is a variant of Deobandism, but is more Salafist than the Wahhabi position. Al-Qaeda's theological background also is not a strict derivative of Wahhabism, but more of the work of Sayyid Qutb, whom many Wahhabi experts consider a heretic.