Detecting, locating, and tracking people in a dynamic environment is important in many applications, ranging from security and environmental surveillance to assistance to people in domestic environments, to the analysis of human activities. To this end, several methods for tracking people have been developed in the field of Computer Vision using different settings, such as monocular cameras, stereo sensors, multiple cameras. In this article we describe a method for People Localization and Tracking (PLT) based on a calibrated fixed stereo vision sensor, its implementation and experimental results. The system analyzes three components of the stereo data (the left intensity image, the disparity image, and the 3-D world locations of measured points) to dynamically update a model of the background; extract foreground objects, such as people and rearranged furniture; track their positions in the world. The system is mostly suitable for indoor medium size environments. It can reliably detect and track people moving in an medium size area (a room or a corridor) in front of the sensor with high reliability and good precision.