The shape analysis performed by our brain is very complex, but it is performed so quickly and in such a natural way that we usually don't think about this intrinsic complexity. Hence, although "to see and understand" seems to be natural and straightforward, the design of versatile and robust computer vision systems is a tough task. Among all different aspects underlying visual information, the shape of objects plays a very important role, which will be emphasized in this book, by showing how such a fundamental feature can be efficiently used to solve a wide range of relevant problems in Computer Vision, Pattern Recognition and Computer Graphics, in both the 2-D and 3-D realms.