The task of detecting, tracking and even inferring the intention of pedestrians in the scene is a very challenging topic. As a proof of the challenge it represents a plethora of research papers that have been presented during the last decades, which have progressively enriched the state of the art with faster and improved detectors. At this moment the first vehicles incorporating pedestrian detectors are being presented for mass production. In this chapter we coarsely summarize the evolution of this research field describing the most advanced current techniques and where the research community is now. Next, we detail the challenges that still need to be addressed to improve current PPSs capabilities.