The Whomping Willow is a very large magical tree in the fictional world of Harry Potter.

Harry and Ron Weasley first discovered the existence of the Whomping Willow just before the start of their second year at Hogwarts. Ron accidentally crashed his father's flying car into the tree, which started trying to destroy the car and the boys.

Harry, Ron and Hermione discovered in their third year that the tree had actually been planted the year that Remus Lupin came to school at Hogwarts, and in fact had been specifically planted for him. Lupin was a werewolf and every month during the full moon, would go to the Whomping Willow, press a knot at the bottom of the enchanted tree, and decend down a tunnel beneath it.

The tunnel leads to the Shrieking Shack , thought to be the most haunted place in all Britain. This was due to Lupin's own shrieking as he made the painful transformation every 28 days and ran around the house biting himself.

The Whomping Willow covers one of only a few remaining secret passages into and out of the Hogwarts, and only a handful know its secret. Most students stay far away from the Willow, as it lashes out at anyone who comes too close or upsets it.