This book constitutes the refereed proceedings of the 19th Conference of the Canadian Society for Computational Studies of Intelligence, Canadian AI 2006, held in Québec City, Canada in June 2006. The book presents 47 carefully reviewed, revised full papers. These are organized in topical sections on agents, bioinformatics, constraint satisfaction and distributed search, knowledge representation and reasoning, natural language, reinforcement learning and, supervised and unsupervised learning.