This volume features work on learning by researchers in various disciplines who share an interest in the systematic study of cognition and in the study of the formal and semantic aspects of language acquisition. A recurring theme is that language learning involves the acquisition of certain competencies and the formation of a system of beliefs which are significantly underdetermined by the linguistic and nonlinguistic inputs available to the learner. Theories of language learning must confront the epistemological problem of how it is possible to induce and fixate a belief-system on the basis of exposure to limited data. A typical strategy in dealing with this problem has been to specify various types of formal and empirical constraints on linguistic and conceptual development in terms of specific hypotheses about the character of what is learned and about the kinds of resources and strategies available to the learner. Most of the contributions in this volume are concerned with the specification and evaluation of such constraints.