Abstract: Frequently a user’s information needs are stored in the databases of multiple search engines. It is inconvenient and inefficient for an ordinary user to invoke multiple search engines and identify useful documents from the returned results. To support unified access to multiple search engines, a metasearch engine can be constructed. When a metasearch engine receives a query from a user, it invokes the underlying search engines to retrieve useful information for the user. Metasearch engines have other benefits as a search tool, such as increasing the coverage of the Web and improving the scalability of the search. In this paper, techniques are surveyed, which are proposed to tackle the database selection problem in a metasearch engine environment. Database selection is to identify search engines that are likely to return useful documents to a given query.