Many languages have morphosyntactic systems that impose a classification on their nominal lexicon. The nature of these systems varies widely, ranging from large systems of lexico-syntactic numeral classifiers, as known from East and South East Asian languages, to highly grammaticalized gender agreement systems of, e.g. European languages (see Aikhenvald 2000 for a comprehensive overview). These systems are also often internally complex, heterogeneous, and descriptively challenging. The morphology, syntax, and semantics of nominal classification bear ample material for interesting research questions in, e.g. typology and historical linguistics. This article reviews some basic features of nominal classification and discusses a number of selected issues that are particularly relevant for ongoing discussions and future research: How can nominal classification systems be typologized according to morphosyntactic criteria (Section 2)? What are the semantic principles of nominal classification and how do they relate to culture and cognition (Section 3)? How does nominal classification diachronically develop and diffuse across languages (Section 4)?