Opinion-Driven Matrix Factorization for Rating Prediction -- Learning Likely Locations -- Evaluation of Attention Levels in a Tetris Game Using a Brain Computer Interface -- Comparing and Combining Eye Gaze and Interface Actions for Determining User Learning with an Interactive Simulation -- Inform or Flood: Estimating When Retweets Duplicate -- Understanding Email Writers: Personality Prediction from Email Messages.

This book constitutes the thoroughly refereed proceedings of the 21st International Conference on User Modeling, Adaption, and Personalization, held in Rome, Italy, in June 2013. The 21 long and 7 short papers of the research paper track were carefully reviewed and selected from numerous submissions. The papers cover the following topics: recommender systems, student modeling, social media and teams, human cognition, personality, privacy, web curation and user profiles, travel and mobile applications, and systems for elderly and disabled individuals.