Intelligent Design is the theory that life did not evolve in the manner stated in Darwin's Theory of Evolution (which is an undirected process), but rather that a "Supreme Being" (who is never identified by a specific name but often believed to be the God of the Christian faith) deliberately guided their creation.  The theory rests on the premise that there are some life forms (such as humans) that are too complex to have been formed through the directionless process of evolution.