Abu Sayyaf (ASG), officially known by the Islamic State as the Islamic State – East Asia Province, also known by its full name, Al Hamas Harakat Al Muqawamah Al Islamiyyah or simply Al Harakat Al Islamiyya, was a Jihadist militant and pirate group that followed the Wahhabi doctrine of Sunni Islam. It was based in and around Jolo and Basilan islands in the southwestern part of the Philippines, where for more than five decades, Moro groups had been engaged in an insurgency seeking to make Moro Province independent. The group was considered violent and was responsible for the Philippines' worst terrorist attack, the bombing of the MV Superferry 14 in 2004, which killed 116 people. The name of the group was derived from Arabic abu (أبو; "father of"), and sayyaf (سيّاف; "swordsmith"). As of April 2023^[update], the group was estimated to have about 20 members, down from 1,250 in 2000. They used mostly improvised explosive devices, mortars and automatic rifles in their attacks.

The group has carried out bombings, kidnappings, assassinations and extortion. It has been involved in criminal activities, including rape, child sexual assault, forced marriage, drive-by shootings and drug trafficking. The goals of the group "appear to have alternated over time between criminal objectives and a more ideological intent".

The group was designated a terrorist group by Australia, Canada, Indonesia, Japan, Malaysia, the Philippines, the United Arab Emirates, the United Kingdom and the United States. From January 15, 2002, to February 24, 2015, fighting Abu Sayyaf became a mission of the American military's Operation Enduring Freedom and part of the Global War on Terrorism. Several hundred U.S. soldiers were stationed in the area primarily to train Filipino troops in counter-terror and counter-guerrilla operations, but, following a status of forces agreement and under Philippine law, they were not allowed to engage in direct combat.

The group was founded by Abdurajak Abubakar Janjalani, and led after his death in 1998 by his younger brother Khadaffy Janjalani until his death in 2006. On July 23, 2014, Isnilon Hapilon, one of the group's leaders, swore an oath of loyalty to Abu Bakr al-Baghdadi, the leader of the Islamic State (IS). In September 2014, the group began kidnapping people for ransom, in the name of the IS.

Since the "All-Out-War" directive was issued in 2019 during the term of President Rodrigo Duterte over continuous attacks perpetrated by Abu Sayyaf towards civilians, especially after the Jolo Cathedral bombings, this has greatly diminished the terror group, with many of their leaders and members being killed and arrested, while former followers who returned to normal lives were reintegrated into society after serving their time in prison and undergoing rehabilitation. On March 22, 2024, the AFP's Western Mindanao Command (WESTMINCOM) announced that the Abu Sayyaf group had been dismantled.

In the early 1970s, the Moro National Liberation Front (MNLF) was the main Muslim rebel group fighting in Basilan and Mindanao. Abdurajak Abubakar Janjalani, the older brother of Khadaffy Janjalani, had been a teacher from Basilan, who studied Islamic theology and Arabic in Libya, Syria and Saudi Arabia during the 1980s. Abdurajak went to Afghanistan to fight against the Soviet Union and the Afghan government during the Soviet–Afghan War. During that period, he was alleged to have met Osama bin Laden and been given $6 million to establish a more Islamic group drawn from the MNLF. Both Abdurajak Abubakar and Khadaffy were natives of Isabela City, one of the poorest cities of the Philippines and capital of Basilan.

In the early 1990s, the MNLF moderated into governing the Autonomous Region in Muslim Mindanao, becoming the ruling government in majority Muslim areas of Mindanao in 1996. When Abdurajak returned to Basilan in 1990, he gathered radical members of the old MNLF who wanted to resume armed struggle and in 1991 established the Abu Sayyaf. Janjalani was funded by a Saudi Islamist, Mohammed Jamal Khalifa, who came to the Philippines in 1987 or 1988 and was head of the Philippine branch of the International Islamic Relief Organization foundation. A defector from Abu Sayyaf told Filipino authorities, "The IIRO was behind the construction of Mosques, school buildings, and other livelihood projects" but only "in areas penetrated, highly influenced and controlled by the Abu Sayyaf". According to the defector, "Only 10 to 30% of the foreign funding goes to the legitimate relief and livelihood projects and the rest go to terrorist operations". Khalifa married a local woman, Alice "Jameelah" Yabo.

By 1995, Abu Sayyaf was active in large-scale bombings and attacks. The first attack was the assault on the town of Ipil, Zamboanga del Sur in April 1995. This year marked the escape of 20-year-old Khadaffy Janjalani from Camp Crame in Manila along with another member named Jovenal Bruno. On December 18, 1998, Abdurajak was killed in a gun battle with the Philippine National Police in Basilan. He was thought to have been about 39.