A pyramid is a stack of image representations with decreasing resolution. Many image processing algorithms run on this hierarchical structure in O(log(n)) parallel processing steps where n is the diameter of the input image. Graph pyramids are made of a stack of successively reduced graphs embedded in the plane. Such pyramids overcome the main limitations of their regular ancestors. The graphs used in the pyramid May be region adjacency graphs or dual graphs. This paper reviews the different hierarchical data structures and introduces a new representation named combinatorial pyramid.