Abstract: A Web based system provides informational services for assisting customers in selecting products or other types of items from an electronic catalog of a merchant. Users of the system can create and join user communities, such as communities based on user hobbies, localities, professions, and organizations. The system also supports implicit membership communities that are based on email addresses (e.g., all users having a “nasa.com” email address), shipping/billing addresses, and other known user information. Using purchase history data collected for online users, the system automatically identifies and generates lists of the most popular items (and/or items that are becoming popular) within particular communities, and makes such information available to users for viewing. For example, in the context of an online book store users of the nasa.com community may automatically be presented a Web page which lists the bestselling book titles among nasa.