Book excerpt: Plan recognition, activity recognition, and intent recognition together combine and unify techniques from user modeling, machine vision, intelligent user interfaces, human/computer interaction, autonomous and multi-agent systems, natural language understanding, and machine learning. Plan, Activity, and Intent Recognition explains the crucial role of these techniques in a wide variety of applications including: - personal agent assistants - computer and network security - opponent modeling in games and simulation systems - coordination in robots and software agents - web e-commerce and collaborative filtering - dialog modeling - video surveillance - smart homes In this book, follow the history of this research area and witness exciting new developments in the field made possible by improved sensors, increased computational power, and new application areas. - Combines basic theory on algorithms for plan/activity recognition along with results from recent workshops and seminars - Explains how to interpret and recognize plans and activities from sensor data - Provides valuable background knowledge and assembles key concepts into one guide for researchers or students studying these disciplines