This book constitutes the refereed proceedings of the 4th International Workshop on Intelligent Virtual Agents, IVA 2003, held in Kloster Irsee, Germany in September 2003.The 63 revised papers and abstracts presented together with a keynote paper were carefully reviewed for inclusion in the book. The papers are organized in topical sections on interface agents and conversational agents; emotion and believability; expressive animation; embodiment and situatedness; motion planning; models, architectures, and tools; mobile and portable IVAs; narration and storytelling; evaluation and design methodologies; and education and training.