This volume brings together a number of papers dealing with various aspects of the study of language acquisition and language learning. The intention is to overcome barriers imposed by restrictions in the accessibility of both publishing sources (journals, conference reports, working papers) as well as languages. Therefore, all papers are in English. Those originally written in German have been translated. The papers originated between 1970 and 1980. They derive from long-term investigations which began 1968 at the University of Freiburg and which were continued since 1969 at the University of Kiel. The essential theme is the nature of man's language learning system, i.e. the ability which allows human beings to learn, and to be taught, natural languages. This ability is unique to human beings; it is species specific; and very likely biologically endowed, i.e. innate. One of the major concerns throughout these papers is to show that learning a foreign language in the classroom via foreign language teaching is by no means totally different from mastering a language in natural situations. Foreign language teaching must be integrated into a comprehensive view of language learning which includes all types of language acquisition.