Harakat al-Shabaab al-Mujahideen, more commonly known as al-Shabaab, is a Salafi-jihadist military and political organisation based in Somalia and active elsewhere in East Africa. It is actively involved in the ongoing Somali Civil War and incorporates elements of Somali nationalism into its Islamist cause. Allegiant to the militant pan-Islamist organization al-Qaeda since 2012, it has also been suspected of forging ties with al-Qaeda in the Islamic Maghreb, and al-Qaeda in the Arabian Peninsula.

Formed in the mid-2000s as part of the Islamic Courts Union, al-Shabaab came to prominence during the 2006–2009 Somalia War, during which it presented itself as a vehicle for the waging of armed resistance against Ethiopia. In subsequent years, it gained popular support from Somalis and became a dominant force in south and central Somalia, defending large swathes of territory by fighting against the African Union Mission to Somalia and the Federal Government of Somalia, as well as the latter's transitional predecessor. The group has also frequently clashed with the Somali Sufi militia Ahlu Sunna Waljama'a as well as with the Islamic State in Somalia. Al-Shabaab gained international prominence due to its recruitment of foreign fighters, including fighters who are from Western countries. Countries which include the United States, the United Kingdom, and the United Arab Emirates, have all designated it as a terrorist organization, and the United States has militarily intervened in order to fight against the group.

Between 2011 and 2013, a coalition which mostly consisted of East African forces, led by the Somali government, wrested a significant amount of territory from al-Shabaab, including the capital city, Mogadishu. During the same period, the group was plagued by internal conflicts over its leadership and ideological direction, which intensified when, in February 2012, al-Shabaab's leadership pledged allegiance to al-Qaeda. It suffered further military losses in 2014, as a result of Operation Indian Ocean, and the killing of its emir, Ahmed Abdi Godane, in an American drone strike, as well as the killing of other leaders. For several years thereafter, al-Shabaab retreated from the major cities, but it remained influential in many rural areas, and it prioritized guerrilla and terror attacks over territorial acquisitions. It is responsible for many high-fatality attacks, including the 2013 Westgate shopping mall attack in Nairobi, Kenya, the October 2017 Mogadishu bombings, the December 2019 Mogadishu bombing, and the October 2022 Mogadishu bombings. In addition to being active in Somalia, it is also active in other East African countries, especially in Kenya, and occasionally also in Ethiopia. Attendant to its recent resurgence, it was estimated to have increased its combat strength to between 7,000 and 12,000 fighters in February 2022.