Motion segmentation is an essential process for many computer vision algorithms. During the last decade, a large amount of work has been trying to tackle this challenge, however, performances of most of them still fall far behind human perception. In this paper the motion segmentation problem is studied, analyzing and reviewing the most important and newest techniques. We propose a classification of all these techniques into different categories according to their main principle and features. Moreover, we point out their strengths and weaknesses and finally we suggest further research directions. Keywords. Computer Vision, Motion Analysis, Motion Segmentation