Аннотация:A novel definition of the 3D curve-skeleton is presented. Many existing approaches to the problem can be formalized in the given definition. The main advantage of the presented mathematical model is that it allows strict quality assesment of the produced curveskeleton. The definition is based on the usage of fat curves. A fat curve is a 3D object which allows to approximate tubular fragments of the shape. A set of fat curves is used to approximate the entire shape; such a set can be considered as a generalization of the 2D medial axis. An example algorithm which obtains curve-skeletons due to the given definition is also presented. The algorithm is robust and efficient.