The chemical space is a concept used primarily in cheminformatics, but it indirectly relates to all fields that deal with chemical structures, from general chemistry up to patent law. It is a theoretical space consisting of all energetically stable (and thus possible) isomers of all chemical structures. This space can be arranged by any number of various criteria to create a projection, within which interesting areas can subsequently be searched, delimited and sampled. In practice, such interesting areas are usually those associated with desired biological activity, synthetic accessibility or patent coverage of contained structures. This article introduces the concept of chemical space in an interdisciplinary context and describes the commonly used forms of its representation.