Knowledge of number names is a subpart of our knowledge of language. This entry discusses various components of this knowledge, placing a special focus on the internal structure of number names and on their morphological marking. The following issues are addressed: the categorial nature of number names; the computational system underlying the formation of complex number names; the structural position of (components of) number names; the various morphophonological and morphosyntactic operations that are operative on numerals such as suppletion, contraction, and (c)overtness of functional heads; the formation of ordinals and the formation of counting numerals. The phenomenon of number names is considered from a comparative‐linguistic perspective: number names from both classifier languages and non‐classifier languages (macro‐variation) are discussed. Furthermore, certain formal phenomena related to number names are discussed from a cross‐dialectal (microvariation) and intra‐linguistic perspective. At a more general level, this chapter aims to show that there is a system of rules – a grammar – that underlies the formation of number names in human language.