The purpose of this critical review was to synthesize the existing research on cognitive development in dual language learners and to identify the gaps and methodological concerns present in the existing research. Studies conducted over the last 30 years have demonstrated that the experience of speaking two languages has positive consequences for the development of several cognitive processes. However, what remains unclear is which cognitive abilities are affected by bilingualism and which are not, if these effects are further influenced by the languages involved, and the extent to which factors such as language proficiency, language of instruction and age of acquisition, moderate the effects of bilingualism. Given that dual language exposure and bilingualism are relatively common experiences for children, identifying the abilities that are affected by bilingualism has important implications for the theoretical understanding of cognitive development and for the design of educational programs for dual language learners. The study includes peer-reviewed articles from 2000-2013 with a focus on typically-developing dual language learners from birth through age six. The search resulted on 187 articles from which 102 met all review criteria. (author abstract)