Topic maps received great attention at many XML conferences and other events since their publication as ISO standard in 2000 and their XML-isation as XTM in 2001. Most of the conference presentation related to topic maps were about the technology and not about the applicability of the technology. We heard about proper handling of scope, published subjects, graph theory, constraints, query languages, and the like. But we have rarely heard how to apply topic maps in a real-world solution and which role topic maps are able to play in such a solution. Consequently, this paper is about topic maps as part of the larger picture of a holistic solution. After providing typical topic maps applications we introduce the three major categories of topic map applications and illustrate them with examples.