Acquisition of negation in Italian as a second language (L2) is investigated on the basis of the longitudinal data of five learners with different first languages (L1s) in the framework of a functional approach focusing on the semantic and pragmatic principles governing the organization of learner varieties and the process of their complexification. Negation develops in a cumulative process in four successive stages. New constructions entering into interlanguage (IL) at each stage effect reduction in frequency of use of previous constructions that specialize for special functions, such as constituent negation. The acquisition process provides insight into some of the mechanisms involved in the processing and filtering of grammatical elements from the input and into strategies employed by the learners to integrate the expression of the scope of negation into the syntactic organization of their variety. The results contribute to a better understanding of the acquisition processes of negation in L2s, allowing the comparison of the development of a relatively straightforward target with an invariable preverbal particle, Italian, with the better investigated development of the complex patterns of English and German.