The moon gains orbital angular momentum at the expense of the earth's rotational angular momentum; the result is the moon gets farther away, and the earth's spin slows down. I'm sure RA will explain the details when he gets back online later today.....
Currently, the evidence points to a catastrophic collision of another body with the Earth not long after the formation of the Earth. This collision is what is believed to have formed the Moon. Originally the Moon was much closer to the Earth and its period did not match its rotation. Over the years the Moon has become tidally locked with the Earth resulting in the Moon keeping one face to the Earth (Its rotation on its axis matches the period of its orbit). This tidal locking will eventually cause the Earth and Moon to keep one face to each other since the Earth is affected by tides as well. (However, under current stellar evolutionary theory, the Sun will go nova before this happens)
Here is a more in depth explanation. The total angular momentum of the earth moon system, which is spin angular momentum plus the orbital angular momentum, is constant. (The Sun plays apart also) Friction of the oceans caused by the tides is causing the Earth to slow down a tiny bit each year. This is approximately two milliseconds per century causing the moon to recede by about 4 centimeters per year. As the Earth slows down, the Moon must recede to keep the total angular momentum a constant. In other words as the spin angular momentum of the earth decreases, the lunar orbital angular momentum must increase. Here is an interesting side note. The velocity of the moon will slow down as the orbit increases.
Another example of tidal locking is the orbit period and rotation of the planet Mercury. What is interesting about this one is that instead of a 1:1 synchronization where Mercury would keep one face to the Sun at all times, it is actually in a 2/3:1 synchronization. This is due to the High eccentricity of its orbit.
There also can be more than one body “locked” to each other. Lets take a look at the moon Io. Io is very nearly the same size as the Earth’s moon. It is approximately 1.04 times the size of the moon. There is a resonance between Io, Ganymede, and Europa. Io completes four revolutions for every one of Ganymede and two of Europa. This is due to a Laplace Resonance phenomenon. A Laplace Resonance is when more than two bodies are forced into a minimum energy configuration. Currently, the evidence points to a catastrophic collision not long after the formation of the Earth. This collision is what is believed to have formed the Moon. Originally the Moon was much closer to the Earth and did not face one side to us like it does now. It has been receding ever since.