With the massive number of cameras have been widely deployed in past few years, human activity analysis has attracted great interest from computer vision researchers and become a hot research area due to its promising applications in many areas such as automated visual surveillance, computer-human interactions, and motion-based identification and diagnosis. However, to detect, categorize and recognize human activity from video is a complicate and difficult problem. This book presents techniques in two topics: general human activity recognition and human activity analysis for the purpose of identifying pathological gait based on symmetry analysis. This book should help shed some light on this research area, and should be especially useful to professionals working in this field, or anyone else who may be considering utilizing video for human activity analysis.