This book constitutes the refereed proceedings of the 8th International Conference on User Modeling, UM 2001, held in Sonthofen, Germany in July 2001.The 19 revised full papers and 20 poster summaries presented together with summaries of 12 selected student presentations were carefully reviewed and selected from 79 submissions. The book offers topical sections on acquiring user models from multi-modal user input; learning interaction models; user models for natural language interpretation, processing, and generation; adaptive interviewing for acquiring user preferences and product customization; supporting user collaboration through adaptive agents; student modeling; and adaptive information filtering, retrieval, and browsing.