随着“以人为中心计算”的兴起和生活中不断涌现的新应用，动作识别和行为理解逐渐成为计算机视觉领域的研究热点。主要从视觉处理的角度分析了动作识别和行为理解的研究现状，从行为的定义、运动特征提取和动作表示以及行为理解的推理方法3个方面对目前的工作做了分析和比较，并且指出了目前这些工作面临的难题和今后的研究方向。

As the “Human-centered computing” is getting more popular and novel applications are evolving, action recognition and activity understanding are attracting researchers in the field of computer vision. In this paper, we review the state-of-the-art work on action and activity analysis with focus on three parts: Definition of activity, low-level motion features extraction and action representation, and reasoning method for activity understanding. Furthermore, open problems for future research and potential directions are discussed.