The three-dimensional (3D) skeleton is developed as a geometric modeling tool. The relationship of the Voronoi diagram to the skeleton is exploited to produce a new 3D skeleton algorithm. This algorithm has several substantial advantages over existing 3D skeleton computation techniques. For instance, the resulting skeleton is a graph that contains coordinate and disk radius information sufficient for exact regeneration, yet it is also amenable to graphical display and further analysis. The resulting skeleton is also homotopically equivalent to the original shape. It is based on the Euclidean metric and requires only a discrete sample set of the shape boundary as input. The new algorithm also reveals deficiencies in the underlying theory of the 3D skeleton. The process of removing these deficiencies leads to the discovery of a new general relationship between local skeleton structure and boundary features which is then exploited to classify and simplify the skeleton.