Ironically, not enough data is also a challenge for recommender systems, which must collect enough data to make effective recommendations for new customers. Sites can make good recommendations faster if they share information about their customers with other sites. Shared information benefits customers who receive more accurate recommendations in less time. Sites that use shared information benefit because the better recommendations help their customers find more products to purchase and because the customers prefer to return to stores with the better recommendations. Large sites that have a wide variety of customer data tend to prefer not to share the data with competitors because they feel having the data gives them a competitive advantage. Smaller sites can band together to overcome this competitive disadvantage by sharing customer data. Further, a consortium of non-competing sites may form with the goal of sharing data to increase the value to companies within the consortium. Customers of sites that share data will need assurances that their privacy will be carefully protected, even as their data are shared beyond the boundary of a single site. The appendix discusses privacy issues in recommender systems.