This paper will focus on a basic social contradiction, due to a deep, often overlooked tension between capitalism, the main motor of the main world, and an influential form of Islam, which, in applying the Protestant term of religious ‘fundamentalism’ I will be calling ‘Islamic fundamentalism’. I believe that this contradiction, which is largely due to the unfettered expansion of increasingly globalized economic capitalism, lies at the root of 9/11. This paper begins by reviewing theories of 9/11 associated with the names of George W. Bush, Samuel Huntington and Bernard Lewis. It argues against the approach to 9/11 in terms of religious or cultural explanation in calling attention to the eco-nomic component of the problem. It is further argued that 9/11 can best be un-derstood as social contradiction between capitalism and Islamic fundamental-ism. It is suggested that this social contradiction indicates an important limit of capitalism.