Key terms for similar passages from a large corpus are identified and used to enhance searching and browsing the corpus. The corpus contains multiple documents such as the text of books. Browsing by concept is supported by identifying a set of similar passages or quotations in documents stored in the corpus and assigning key terms to passages which links conceptually related passages together. The context of each passage instance is identified and can include, for example, the text surrounding the passage. The contexts of all similar passage instances are analyzed in order to identify key terms for the similar passage. The related key terms are analyzed to identify relationships among the key terms from different similar passage sets. The key terms can be used as a basis for navigating the documents in the corpus. The key terms enable browsing the documents in the corpus by concepts referenced in the documents.