A search engine is an internet site that allows users to enter a search query and then lists a series of sites that match the query. A tool that consists of a database of websites that help users find web pages on a given subject based on a query for a specific key phrase. Web search engines such as Google consist of organic (free) and paid listings. In terms of market share in 2007, Google is the leader at around 54% followed by Yahoo and Microsoft Live Search.