Where did the Moon come From?

There have been several theories for the origin of the Moon. The strongest data currently supports the "Giant Impact" theory. See the links below for more.
https://www.psi.edu/epo/moon/moon.html

http://phys.org/news/2012-10-massive-planetary-collision-zapped-key.html

http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question38.html