While not all of the planets rotate on their individual axes in the same direction — Uranus and Venus both rotate opposite to the other six planets — the planets are in agreement as to which way to go. The shared motion is an artifact of the formation of the solar system from a giant rotating gas cloud 4.5 billion years ago.
As for the reversed, or retrograde, spin of Uranus and Venus, scientists are divided as to the cause. Most subscribe to the theory that early in their histories, these worlds were subjected to massive collisions with planetary-sized objects, so powerful they reversed the planets original direction of rotation — and in the case of Uranus, knocked it almost completely sideways.