Encyclopedia of Machine Learning Chapter No: 00338 Page Proof Page 1 22-4-2010 #1 R Recommender Systems Prem Melville, Vikas Sindhwani Machine Learning, IBM T. J. Watson Research Center, Route /P.O. Box , Kitchawan Rd, Yorktown Heights, NY , USA Definition The goal of a recommender system is to generate mean- ingful recommendations to a collection of users for items or products tha