This book constitutes the thoroughly refereed post-proceedings of the First International CLEAR 2006 Evaluation Campaign and Workshop on Classification of Events, Activities and Relationships for evaluation of multimodal technologies for the perception of humans, their activities and interactions, held in Southampton, UK, in April 2006.The 29 revised full system description papers and 1 institutional paper presented together with 2 invited papers were carefully reviewed and selected for inclusion in the book. CLEAR is an international effort to evaluate systems that are designed to analyze people's identities, activities, interactions and relationships in human-human interaction scenarios, as well as related scenarios. The papers are organized in topical sections on 3D person tracking, 2D face detection and tracking, person tracking on surveillance data, vehicle tracking, person identification, head pose estimation, acoustic scene analysis, and other evaluations.