Methods, systems, and apparatus, including computer program products, for ranking search results of a search query using corpus search statistics. In one aspect, a method includes determining a first relevance of a first corpus to a search query, determining a second relevance of a second corpus to the search query, determining a measure of relative relevance of the first corpus and the second corpus to the search query, and providing the measure of relative relevance to a ranking engine for ranking of search results for a new search corresponding to the search query.