Wikipedia can be utilized as a controlled vocabulary for identifying the main topics in a document, with article titles serving as index terms and redirect titles as their synonyms. Wikipedia contains over 4M such titles covering the terminology of nearly any document collection. This permits controlled indexing in the absence of manually created vocabularies. We combine state-of-the-art strategies for automatic controlled indexing with Wikipedia’s unique property — a richly hyperlinked encyclopedia. We evaluate the scheme by comparing automatically assigned topics with those chosen manually by human indexers. Analysis of indexing consistency shows that our algorithm performs as well as the average person.