In the last few decades, there has been increased interest in the incorporation of data from bi- and multilingual individuals in linguistic theory: from second language acquisition and language attrition to heritage varieties and code-switching. This dissertation discusses a range of ways in which code-switching data can provide insight into the mechanisms that underlie linguistic structures. The data will be analysed within the framework of Minimalist Generative syntax and Distributed Morphology.The first part investigates grammatical gender assignment in code- switching between English, a language without grammatical gender, and two languages with grammatical gender: French and Belgian Dutch. These languages have comparable, but different gender systems. French has two genders: masculine and feminine, whereas Belgian Dutch adds a third: neuter. The study in this part of the dissertation compares gen- der assignment strategies in bilinguals with different profiles. In addition, the code-switching data provide evidence against the default status of neuter in Belgian Dutch.The second part focuses on word order and includes two studies: one on verb-second word order in Dutch-English code-switching and one on adverb placement in English-French and Dutch-English code- switching. The verb-second chapter identifies a lacuna in the traditional Generative analysis for verb second and uses the CS data to address this. The chapter on adverb position looks at placement of the adverb between the verb and its direct object, which is allowed in Dutch and French, but not in English. For all domains investigated, it is found that the finite verb predicts word order.Taken together, these studies demonstrate that bilingual data can shine a light on elements of the theory of grammar which remain in the shadows when only monolingual data is used. ; Les dernières décennies ont vu croître l’intérêt pour l’intégration à la réflexion en linguistique théorique des données produites par des locuteurs/trices bilingues ou multilingues, que ...