Methods, systems and apparatus, including computer program products, for ranking expertise. In some implementations a method is provided that includes identifying a plurality of identities, and identifying a plurality of topics using one or more documents in a repository. For a document in a corpus of documents identifying one or more occurrences of any identity in the plurality of identities and one or more occurrences of any topic in the plurality of topics, determining an association between the identities occurring in the document and the document including deriving an identity score for each unique identity occurring in the document, determining an association between the topics occurring in the document and the document including deriving a topic score for each unique topic occurring in the document, and using the determined associations to derive a score of the document with respect to identities and topics occurring in the document.