The assumed connection between ease of language learning and age has been investigated in recent years by researchers from a wide range of disciplines. With the exception of the findings of research that authentic accents are more easily acquired by children, studies seem to indicate that efficiency in language learning increases with maturation. Evidence does not indicate that there is a firm qualitative distinction to be drawn between the respective ways in which children and adults master a second language. However, much thinking of theorists in second language acquisition has been based on the assumption that children are more efficient second-language learners. Results of this theorizing are outlined under the following headings: (1) imprinting; (2)lateralization and cerebral plasticity; (3) the thalamus theory; (4) the cognitive developmental hypothesis; and (5) affect and motivation differences between children, adolescents, and adults. It is concluded that the evidence for a general age-related deterioration in the capacity to learn a second language is scanty. Of the theories proposed, those which seem to be most consistent with the evidence are those which do not assume a sharp cut-off point for all aspects of language acquisition. (AMH)