links to various articles, and the online photo management and sharing site Flickr hosts more than 250 million photos. This problem of having too many choices to be able to find the right ones is known as information overload Recommende ms are ont particular, recommender systems have been shown to help users find items of interest from among a large pool of potentially interesting items. Recommender systems bring mutual benefits to both users and operators of the sites with information overload. Users benefit as they do not have to sift through hundreds of thousands of available items to find interesting items. In addition, many recommender systems are, at least in part, proactive in nature in that they automatically populate a list of personalized recommendations based on the user's preferences and other similar users'input. The user may discover many new items she is curious to explore from the recommendations. On the other hand, e-commerce sites that employ recommender systems can increase sales revenue in at least two ways: a) by drawing customers'attention to items that they are likely to buy, and b) by cross-selling items. Netflirs, an online DVD rental service that uses a recommender system, is a good example of this-the] average Netfix customer rents seven DVDs a month, three times the rate at brick-and-mortar stores"(Anderson 2004). And"between 70 and 80 percent of Netflix rentals come from the company's back catalog of 38,000 films rather than recent eleases, 6 Netfix benefits because the old releases are cheaper, and the customer demand is not concentrated only on the expensive latest releases. Clear benefits like this are probably thereasonswhysomanye-commercesites-amazon.comitunEs.com,last.fm,netfix.com pandora.com,justtonameafewhavebeenmakingrecommendersystemsintegraltotheir operations. We are experiencing, more than ever, phrases such as"Get Recommendations Albums for You?,"Customers who bought items in your Shopping Cart also bought"in chttp://www.fickr.cor http://www.netfix.com http://www.nytimes.com/2006/01/23/technology/23recommend.html Reproduced with permission of the copyright owner. Further reproduction prohibited without permissionReproduced with permission of the copyright owner. Further reproduction prohibited without permission