This book presents four closely related reports on the lay-out, data collection and results of a research project on the acquisition of German as a Foreign Language by adult students. A critical description is given of the course of the extensive data collection and the successes and difficulties encountered. This is followed by a theoretical paper in which a model of the production process in second language performance is postulated and discussed. Sections three and four describe analyses of spontaneous self-corrections as evidence of the learner's control of his speech process, which takes into account the influence of individual and linguistic variables.