When learners approach a foreign language, there are many factors which affect the way they deal with the new language. These factors include personal characteristics of learners, typological similarities/differences between the target language and the previously known languages and the context in which the language is used. Hence, the purpose of this study is to investigate the interaction between age, proficiency and task-type in determining the occurrence of lexical transfer. Specifically, the study focuses on the effect of this interaction on cross-linguistic influence in using content and function words by Moroccan EFL learners. Another objective is to investigate the qualitative difference between L1- and L2-based lexical transfer by determining the source of crosslinguistic influence: L1 Moroccan Arabic or L2 French.