What causes the moon to change it's shape?

Answer 1

The moon does not change shapes. The shadow of the earth on the moon changes how much of it you can see.

Another viewpoint: I think this question is about the "phases" of the Moon.

The Moon only appears to change shape during its different phases.

Exactly one half of the Moon is in sunlight at any time. The phases occur because the Moon orbits Earth. That causes us to see different amounts of the sunlit Moon, and so its shape seems to change.

Answer 2

The changing shape of the moon, known as its phases, is caused by its position relative to the Earth and the Sun. As the moon orbits the Earth, the amount of sunlight reflecting off its surface that we can see changes. This creates the different phases of the moon, such as full moon, new moon, waxing crescent, and waning gibbous.