One lunar day, the length of time it takes the moon to complete a full rotation on its axis, is equivalent to 28 days on Earth. This is also the amount of time it takes for the moon to complete its orbit around the Earth.
Due to the fact that the moon's rotational period and orbital period are both about 28 days, it deceivingly appears that the moon never rotates. This is the result of the Earth's gravity creating "tidal bulges" on the moon which maintain this slow rotation. Most other moons in the solar system are subject to the same tidal forces and, thus, always show the same face to the planet below.
