Shared databases are used for knowledge exchange in groups. Whether a person is willing to contribute knowledge to a shared database presents a social dilemma: Each group member saves time and energy by not contributing any information to the database and by using the database only to retrieve information which was contributed by others. But if all people use this strategy, then the database will be empty and, hence, useless for every group member. Based on theoretical approaches, two models for fostering the information-sharing behavior of database users are presented. One for enhancing the quality of database contents, and one for enhancing the quantity of those contents. The models take into account the following factors: the kinds of rewards the participants obtain for contributing information, the individual costs associated with this contribution, the prospective metaknowledge about the importance of one's own information to the others, and the retrospective metaknowledge about how much others contributed to and retrieved from the database. These factors enhance the quantity of database contents as well as their quality. A highly controlled experimental setting for testing the models is presented. Results of three experiments support some expectations derived from the models. Their implications for organizational and educational settings are discussed.