This report, the fifth in a series of working papers issued by the Project on Applied Contrastive Linguistics (PAKS) at the University of Stuttgart, is dedicated to a consideration of error analysis in language learning, here seen as relevant not only for the teacher but for the text book writer and the curriculum planner as well. An introduction by Gerhard Nickel, the head of the PAKS project, discusses questions basic to error analysis (here also called -Lapsology-). Articles deal with: intra and interstructural mistakes on the phonemic-graphemic level, error analysis in the realm of morphology and syntax, the anlysis of lexical erros, and error analysis and therapy in the area of the lexicon. A bibliography of relevant publications is also included. Appended teacher reports discuss the use of therapeutic error analysis in the realm of interference and problems arising from the parallel teaching of English and French in German schools. All articles are in German, but references in the bibliography are chiefly to materials in English. (FWB)