Queues work first in, first out. Stacks work last in, first out. If you create two stacks, you can replicate the behavior of a queue by having inserted objects do the following: Check if stack 2 empty If true, enter stack 2 and process If false, add to stack 1 Repeat check if stack 2 empty If true, move stack 1 items to stack 2 If false, wait... This works because when stack 2 is empty and stack 1 is not, the order of the stack is flipped. Thus, first in stack 1 because first out of stack 2.