The acquisition of a second language requires the construction or reconstruction of linguistic knowledge about the new language system. Learners of a second language have to acquire the linguistic structures of the second language by constructing or reassessing their own knowledge in the light of the new one. Some of these new linguistic structures may be more or less complex to process and/or difficult to acquire. In this review, we focus on an example of linguistic complexity in French, namely, the subjunctive. Through a discussion of some selected studies on the second language acquisition of the French subjunctive, our purpose is to argue that these findings, considered from a psycholinguistic perspective, could be fruitful for further research employing neuroscience techniques, such as electroencephalography or neuroimaging in order to better understand the neurocognitive processing of this complex structure both in French native speakers and in learners of French. Hence, we aim to contribute to exploring the question of linguistic transfer in the field of second language acquisition, the typological distance/relation between L1–L2, the syntactic acquisition of complex structures in adult second language learners, and the potential contributions of electroencephalography and functional magnetic resonance imaging to the processing of the subjunctive, selected as an example of linguistic complexity that has not yet received much attention.