A majority of the early research in Second Language Acquisition focused on diachronic variation in the learners’ interlanguage (IL), that is, differences in the IL linked to a supposed increase in knowledge between two points in time (cf. Tarone 1988). The last decade has seen an increase in studies combining a diachronic perspective with a synchronic one, that is, where variation in production is seen as the consequence of individual differences among learners (gender, extraversion, learning strategies, attitudes, motivation, sociobiographical variables linked to the language learning experience and the use of the target language (TL)). In this perspective, non-native-like patterns are not automatically assumed to be the result of incomplete knowledge, but other possible causes are taken into consideration such as temporary inaccessibility of information in stressful situations or even a conscious decision by the L2 user to deviate from the TL norm.