The Milky Way rotates due to the conservation of angular momentum. As the gas and dust that formed the Milky Way collapsed under gravity, it began to rotate. This rotation caused the gas and dust to flatten into a disk, and the disk continued to rotate as it grew in size. The Milky Way's stars and planets all orbit the center of the galaxy in the same direction, which is the direction of the galaxy's rotation.

The Milky Way's rotation is not constant. The stars and gas in the inner part of the galaxy rotate faster than those in the outer part. This is because the gravitational force of the galaxy's central black hole pulls the stars and gas inward, causing them to rotate faster. The Milky Way's rotation is also affected by the gravitational interactions of other galaxies in the Local Group.

The Milky Way's rotation is an important factor in the galaxy's structure and evolution. The rotation helps to keep the galaxy from collapsing under its own gravity, and it also drives the galaxy's spiral structure. The rotation also helps to distribute stars and gas throughout the galaxy, and it plays a role in the formation of stars and planets.