Researchers often point to the work of Cummins (1981), who proposed that two distinct types of language proficiency exist, basic interpersonal communications skills (BICS) and cognitive/academic language proficiency (CALP). BICS includes aspects of language such as basic vocabulary and pronunciation, skills that are readily apparent during conversations between two or more people. In contrast, CALP refers to language skills that allow an individual to process and make meaning of language that exists independent of any situational clues, and is the language skill required for meaningful engagement in most academic tasks. Cummins (1981) proposed that the best way for a student to develop CALP in their second language was to first develop CALP in their primary language. While Cummins made invaluable contributions to one's understanding of second language development and the need for bilingual education, his theory of BICS and CALP is largely descriptive and does not explain the underlying cognitive processes involved in second language development. Vygotsky (1986/1934), writing more than 45 years before Cummins, provides theoretical insight into this process. The acclaimed Russian developmental psychologist describes the use of language as a psychological tool for the purpose of analyzing and solving complex problems. Problem-solving ability, a stage in language development that Vygotsky refers to as "the use of concepts," is essentially the equivalent of Cummins' CALP. In this article, the author talks about a Vygotskian framework for understanding BICS and CALP.