This dissertation investigates the linguistic expression of individuation, counting, quantifying and measuring in Yudja (Juruna family), a Tupi language spoken in Brazil. Based on elicitation data and experimental studies with children and adults, three main topics are explored: (i) the semantic properties of numeral constructions and their compatibility with notional count and notional mass nouns; (ii) the semantics of container phrases and their interaction with numerals, and finally (iii) the semantics of nominal quantifiers. Relying on the principles of mereotopology (Casati and Varzi 1999, Varzi 2007), the main claim of this dissertation is that in Yudja all nouns can be used as count nouns. That is, in Yudja maximal self-connected concrete portions of a kind can be considered as atoms and can be counted. This claim is based on three fundamental properties of Yudja that were confirmed by experimental studies with children and adults. First, data obtained in context-based elicitation sessions show that all notional count and all notional mass nouns can be directly combined with numerals. Second, the results of quantity judgments studies with Yudja children and adults suggest that all nouns can be directly combined with count-quantifiers and that count-quantifiers are necessarily interpreted as referring to the number of concrete portions. Third, the results of comprehension and production tasks with Yudja children and adults show that container phrases are interpreted as locatives and do not necessarily determine the individuation unit. These properties together suggest that all nouns in Yudja are interpreted as count nouns.