Library collections include increasingly large amounts of digital material. Libraries are digitising parts of their collection to provide wider access to important resources, and born-digital material is being added to collections. Basic text string searching and linear chapter-by-chapter browsing functionality is usually provided but so much more is possible. The implicit linkages and cross-references between books, which occur in all print collections, can be made explicit in a collection of electronic texts. Correctly encoded, they create a framework to provide users with the ability to move horizontally between books and collections by following links between topics. Using this approach the New Zealand Electronic Text Centre (NZETC) has explored and developed an improved means of navigation for its growing online digital library using Topic Map technology. Like a simple back-of book index or a library classification system, a topic map aggregates information to provide binding points from which everything that is known about a given subject can be reached.