Literally meaning "the youth," al-Shabab started out as a militia that splintered off from Islamist parties in the mid-2000s. It is known for imposing a strict version of sharia law in areas it controls, including stoning women accused of adultery.
The group first made a name for itself in Somalia as a response to foreign aggression, but lately has been losing ground and is waging campaigns of indiscriminate violence in neighbouring states. It has recently aligned itself with al-Qaeda.
Westgate mall attack
Kenyan authorities were caught off guard when gunmen rampaged through the glitzy shopping centre, targeting foreigners and killing more than 70 people. Al-Shabab claimed responsibility.
The United Nations estimates more than 250,000 people – half of them younger than five – starved to death during the famine. At the time, al-Shabab controlled swaths of Somalia and expelled foreign aid workers and charities despite dire need.
Soccer bombings in Uganda
Two bomb blasts killed more than 70 people watching a World Cup soccer match at two locations in Kampala. The attacks were retribution for Uganda's role in a UN-backed peacekeeping force in Somalia.
Co-ordinated car bombs in Somalia
Five co-ordinated suicide attacks were launched in two cities in Somalia in October, 2008, killing at least 26 people.