Abstract
This article looks at the general effects of bilingualism on cognitive development and highlights the specific effects of bilingualism on third language acquisition. First, it examines the effects of bilingualism on cognitive development, metalinguistic awareness and communicative skills and then, it focuses on the specific effects of bilingualism on third language proficiency by discussing the results of several research studies conducted in different settings and contexts. An important distinction is made between studies focusing on the acquisition of general proficiency in the third language and studies that examine specific aspects of third language proficiency. The effects of bilingualism on third language acquisition are discussed as related to the experience acquired by third language learners in the process of second language acquisition and the effects of bilingualism on metalinguistic awareness and communicative skills. These effects are also discussed with reference to the concepts of additive bilingualism(Lambert, 1974), the threshold hypothesis(Cummins,1976) and the distinction between control of attention and analysis (Bialystok, 1991).