In this paper an attempt is made to characterize and contrast aspects of the functional organization of neuropsychological systems carrying outprimary language acquisitionand two distinct types ofnonprimary language acquisition: secondary language acquisition, andforeign language learning.It is noted that foreign language learning is quite different from primary language acquisition, but that between secondary language acquisition and primary language acquisition there seem to be more similarities than differences. One of the most significant differences is that secondary language acquisition is based on neurofunctional systems that are fullyoperationalfor children 6–13, but essentiallymaturefor still older learners. While there is no critical period for secondary language acquisition such as exists for primary language acquisition, there is evidence that younger children are in fact better able to achieve communicative competence in a new language than teens or older adults. Several explanations have been proposed for the existence of what may be called asensitive periodfor secondary language acquisition, and it is concluded here that in addition to a combination of personality variables, affective variables, social variables, cognitive style and environmental circumstances, there still remains an intrinsic neurofunctional basis for the greater facility with which young children achieve secondary language competenc