Background: Bilingualism (or multilingualism), namely functional proficiency in two (or more) languages, is currently the norm for over half of the world’s population. Bilingualism in typically developing (TD) children has been suggested to enhance cognitive and communicative domains crucially corresponding to areas often affected by Autism Spectrum Disorder (ASD), i.e. Metalinguistic Awareness, Executive Functions (EF), Theory of Mind (ToM) and Gestures. Studies on children with ASD, also suggestive of cognitive and communicative benefits associated with bilingualism, are scarce and present limitations that hinder their generalizability. Advantages associated with bilingualism in TD children are also debated, due to mixed findings which may stem from a number of factors, e.g., considering bilinguals at a particular moment in development while advantages may surface at different phases, and considering bilinguals as a monolithic group while variability in specific aspects of the bilingual experience may affect the emergence of enhanced cognitive and communicative functioning. The ABCCD will venture into the barely explored territory at the intersection of ASD and bilingualism and revisit bilingualism in TD children with the objective of addressing the following question: Could bilingualism be beneficial for the development of cognition and communication in ASD and TD? Method: We will carry out an unprecedented large-scale longitudinal study including 150 5-11 year-old children with ASD and 150 TD children of similar nonverbal IQ. Participants will be of varying dual language experiences (timing, quantity, quality of exposure), measured carefully alongside other factors potentially mediating cognitive and communicative outcomes (e.g. socio-economic status, ASD severity, intervention services, etc). The creation of gamified, computerized tasks will allow the assessment of competencies in a motivating and consistent manner, while circumventing various social challenges associated with ASD. Results: We will evaluate the relevance of bilingualism as a predictor of linguistic, metalinguistic, EF, ToM and gestural development, and compare effects between the two groups (ASD and TD) using a linear mixed effect regression, which can integrate both continuous and categorical predictors at all levels of measurement (subject- and time-varying). We expect to uncover aspects of bilingual experiences that indeed boost cognition and communication. Impact: Theoretically, this work promises a substantial breakthrough in our knowledge of the development of the language-cognition interface. On a societal level, results will address the pressing need of parents and professionals to take evidence-based decisions concerning bilingualism in ASD.