This study investigates some instances of linguistic development in the acquisition of a second language that might be subsumed under the issue of grammaticalization. First, the notion of grammaticalization is discussed with reference to the current linguistic debate and its applicability to the domain of language acquisition is evaluated. Then, some cases are examined drawing on data on the acquisition of Italian collected during several years at the University of Pavia. With respect to temporality and modality, learners are shown to move from lexical means or context-dependent strategies to a gradual acquisition of the morphological devices required by the target language. The results of the analyses are discussed in terms of their implications for both general linguistic theory and language acquisition research.