Disclosed are various embodiments for classifying network sites into site categories. A network site is classified into at least one of a plurality of categories based at least in part on similarity. Query popularity, query competitiveness, and/or query importance may be used in determining similarity. The similarity is measured between a first plurality of search queries and a second plurality of search queries. The first plurality of search queries is one that produced first search results that include the network site. The second plurality of search queries is one that produced second search results that include other network sites. Each of the other network sites has a respective category. The query-similarity based scoring may be combined with more scoring based on crawling and processing network page or network site contents.