This paper analyses the expression of number; more precisely, it investigates on which parts of speech and by which linguistic means number is grammatically encoded in Kambaata (Cushitic, Ethiopia). Number is marked, to different degrees, on common nouns, proper nouns and pronouns. Traces of number agreement are found on modifiers and verbs. The core of this paper deals with number marking on common nouns, especially the interaction of number marking with the lexical semantics of certain noun classes. A comparison with the grammatical categories of case and gender shows that number is a grammatical category between inflection and derivation.