Al-Qaeda is a pan-Islamist militant organization led by Sunni jihadists who self-identify as a vanguard spearheading a global Islamist revolution to unite the Muslim world under a supra-national Islamic caliphate. Its membership is mostly composed of Arabs but also includes people from other ethnic groups. Al-Qaeda has mounted attacks on civilian and military targets of the U.S. and its allies; such as the 1998 US embassy bombings, the USS Cole bombing, and the September 11 attacks. It has been designated a terrorist organization by the United Nations and over two dozen countries around the world.

The organization was founded in a series of meetings held in Peshawar during 1988, attended by Abdullah Azzam, Osama bin Laden, Muhammad Atef, Ayman al-Zawahiri and other veterans of the Soviet–Afghan War. Building upon the networks of Maktab al-Khidamat, the founding members decided to create an organization named "Al-Qaeda" to serve as a "vanguard" for jihad. When Saddam Hussein invaded and occupied Kuwait in 1990, bin Laden offered to support Saudi Arabia by sending his Mujahideen fighters. His offer was rebuffed by the Saudi government, which instead sought the aid of the United States. The stationing of U.S. troops in the Arabian Peninsula prompted bin Laden to declare a jihad against both the rulers of Saudi Arabia – whom he denounced as murtadd (apostates) – and against the US. From 1992, al-Qaeda established its headquarters in Sudan until it was expelled in 1996. It then shifted its base to the Taliban-ruled Afghanistan and later expanded to other parts of the world, primarily in the Middle East and South Asia. In 1996 and 1998, bin Laden issued two fatāwā that demanded the withdrawal of U.S. troops from Saudi Arabia.

In 1998, al-Qaeda conducted the US embassy bombings in Kenya and Tanzania, which killed 224 people. The U.S. retaliated by launching Operation Infinite Reach, against al-Qaeda targets in Afghanistan and Sudan. In 2001, al-Qaeda carried out the September 11 attacks, resulting in nearly 3,000 deaths, long-term health consequences of nearby residents, damage to global economic markets, the triggering of drastic geo-political changes as well as generating profound cultural influence across the world. The U.S. launched the war on Terror in response and invaded Afghanistan to depose the Taliban and destroy al-Qaeda. In 2003, a U.S.-led coalition invaded Iraq, overthrowing the Ba'athist regime which they falsely accused of having ties with al-Qaeda. In 2004, al-Qaeda launched its Iraqi regional branch. After pursuing him for almost a decade, the U.S. military killed bin Laden in Pakistan in May 2011.

Al-Qaeda members believe that a Judeo-Christian alliance (led by the United States) is waging a war against Islam and conspiring to destroy Islam. Al-Qaeda also opposes man-made laws, and seek to implement sharīʿah (Islamic law) in Muslim countries. Al-Qaeda fighters characteristically deploy tactics such as suicide attacks (Inghimasi and Istishhadi operations) involving simultaneous bombing of several targets in battle-zones. Al-Qaeda's Iraq branch, which later morphed into the Islamic State of Iraq after 2006, was responsible for numerous sectarian attacks against Shias during its Iraqi insurgency. Al-Qaeda ideologues envision the violent removal of all foreign and secularist influences in Muslim countries, which it denounces as corrupt deviations. Following the death of bin Laden in 2011, al-Qaeda vowed to avenge his killing. The group was then led by Egyptian Ayman al-Zawahiri until he too was killed by the United States in 2022. As of 2021^[update], they have reportedly suffered from a deterioration of central command over its regional operations.

Al-Qaeda only indirectly controls its day-to-day operations. Its philosophy calls for the centralization of decision making, while allowing for the decentralization of execution. The top leaders of al-Qaeda have defined the organization's ideology and guiding strategy, and they have also articulated simple and easy-to-receive messages. At the same time, mid-level organizations were given autonomy, but they had to consult with top management before large-scale attacks and assassinations. Top management included the shura council as well as committees on military operations, finance, and information sharing. Through the information committees of al-Qaeda, Zawahiri placed special emphasis on communicating with his groups. However, after the war on terror, al-Qaeda's leadership has become isolated. As a result, the leadership has become decentralized, and the organization has become regionalized into several al-Qaeda groups.

The group was initially dominated by Egyptians and Saudis, with some participation from Yemenis and Kuwaitis. Over time, it has evolved into a more international terrorist organization. While its core group originally shared a background in Egypt and the Arabian Peninsula, it has since attracted fighters from other Arab groups, including North Africans, Jordanians, Palestinians, and Iraqis. In the decade following the 9/11 attacks, Muslims from non-Arab backgrounds, such as Pakistanis, Afghans, Turks, Kurds, and European converts to Islam, have also joined the organization.

Many Western analysts do not believe that the global jihadist movement is driven at every level by al-Qaeda's leadership. However, bin Laden held considerable ideological influence over revolutionary Islamist movements across the world. Experts argue that al-Qaeda has fragmented into a number of disparate regional movements, and that these groups bear little connection with one another.

This view mirrors the account given by Osama bin Laden in his October 2001 interview with Tayseer Allouni: