CSML is a semantic markup language created for the publishing and sharing of conceptual spaces, which are geometric structures that represent semantics at the conceptual level. CSML can be used to describe semantics that are not captured well by the ontology languages commonly used in the Semantic Web. Measurement of the semantic similarity of concepts as well as the combination of concepts without shared properties are common human cognitive tasks. However, these operations present sources of difficulty for tools reliant upon set-theoretic and syllogistic reasoning on symbolic ontologies. In contrast, these operations can be modeled naturally using conceptual spaces. This paper describes the design decisions behind CSML, introduces the key component elements of a CSML document, and presents examples of its usage.