Why did Hitler attack the Soviet Union in June 1941?

Adolf Hitler's decision to invade the USSR was his most fateful of the entire war. It was this decision that widened the conflict into a global war and ultimately led to the collapse of the Third Reich itself.

This decision continues to be the subject of much debate. What role did strategic factors play? What weight should be given to ideology?

The following numbered outline gives the student a good basis from which to conduct further research into the rationale behind the German invasion of the Soviet Union. I have attached a bibliography for an essay I wrote on this topic.