Al-Qaeda is an armed network of Sunni Muslims with very extreme views.
They have been blamed for a lot of attacks and bombings in different countries all over the world.
They are opposed to a lot of western governments, who have called them a terrorist organisation.
They want countries like the US to stop having influence in the Middle East - particularly in places like Iraq and Israel.
Their leader was a man called Osama Bin Laden. However in May 2011 he was killed by American soldiers.
Although the group claims to be on a holy war, many Muslims say what they are doing is very wrong.
It's thought they are loosely organised, with one al-Qaeda group, or cell, not really knowing very much about another.
The name al-Qaeda means "the base".