The work upon which the present report is based was designed to integrate those aspects of bilingual behaviour which had previously been studied separately. The paper considers two questions. First, what relationships exist among descriptions of bilingualism which employ methods derived from different disciplines? More specifically, to what extent do linguistic, psychological, and sociological measurements co-vary when applied to the same bilingual speakers? Second, what is the relative utility of such measures in terms of their ability to predict, both individually and jointly, the same criterion behaviours ?