Hanoi Tower is a "puzzle" consisting of a base containing three pins, on which one discs are arranged on top of each other in ascending order from top to bottom. The problem is to move all disks from one pin to any other, using one of the pins as an aid, so that a larger disk will never be on top of a smaller one under any circumstances. The number of discs may vary with the simplest containing only three.

Today, the Hanoi Tower has traditionally been regarded as a procedure for assessing working memory capacity, and especially for planning and troubleshooting.