A theory that the evolution of life on Earth was set in motion and/or guided by God.
It's a very rational theory. Unfortunately, it's not taken seriously by either atheists or Christians who believe in Creationism. Atheists don't like because it acknowledges the existance of God, and Christian creationists don't take it seriously because they think it conflicts with the Bible. Actually, theistic evolution is indeed compatible with Scripture. The "Seven Days of Creation," for instance, may not have been actual days, but very long periods of time. Also, the description of Man's creation in Genesis seems to imply some sort of process. And contrary to the concerns of some Christians, theistic evolution does not preclude the existence of the human soul or the distinction between Man and other life on Earth. God could have waited until Man had evolved to the point of sentience, then given them souls and dominion over nature.
Also, theistic evolution's theory of an intelligent power being responsible for the evolutionary process may explain some of the problems of evolutionary theory in general.
Theistic Evolution is distinct from Intelligent Design. While theistic evolution accepts the existence of a Creator on faith, Intelligent Design seeks to prove the Creator's existence.
Atheist: Life on Earth evolved into its present state without the intervention of a Creator.
Christian Creationist: Noooo, it was created in its present state by God in 7 days.
Christian Theistic Evolutionist: Actually, evolution could have been the means by which God created life.
Atheist & Christian Creationist both: That's ridiculous!
Christian Theistic Evolutionist:(sighs) I can't win here.