What is the impact theory of the Moon's formation?

Some hypothetical body - usually named Theia for related mythological reasons, and around the size of Mars - struck the early Earth. the resulting energies flung large amounts of matter into space around the planet, and these later accumulated into the moon as we know it.

It is interesting to point out this would also explain the Earth's axial tilt of nearly 23o and several other facts about the moon's composition. However, like many hypotheses it also cannot account for some other facts and research continues to ascertain whether it ever could.