The paper deals with the development of the Department of German as a Second/Foreign Language at the University Duisburg- Essen. The author begins by tracing the origins and formation of the department up to the present day. DaZ/DaF was established in the seventies by Johannes Meyer- Ingwersen and Rosemarie Neumann, who invented the term DaZ and has worked from 1973 in the area of bilingualism and the linguistic development of Turkish children living in Germany. The term was coined to provide a distinction between DaZ and the existing term DaF, but it also functions as a complement of the older terminology. The author outlines the differences between these two terms: DaF is seen as a controlled acquisition of the second language, whereas DaZ is considered to be uncontrolled acquisition. Other factors playing a role in distinguishing the two phenomena include socio-psychological factors and class affiliation. There are still many similarities between the two areas, so that the department at the University Duisburg-Essen is called “Deutsch als Zweit- und Fremdsprache” (German as a Second- and Foreign Language), reflecting this fact. The author discusses the question of the role of the mother tongue during the socialisation of the migrant children. Unfortunately there have been few surveys in Germany dedicated to the relationship between the first and the second (German) languages during the linguistic development of migrant children. However this topic is important, because the language spoken in the family forms the basis of the cognitive and emotional development of children. In 1992 Baur and Meder surveyed the impact of the classes in mother tongue empirically. They evaluated written assignments of Turkish and Yugoslavian pupils in mother tongue and in the second language (German) by means of a C-Test. The results confirmed the interdependence of the first and second languages in childrens’ development. In 2002 during the so called SPREEG studies, children in Essen’s primary schools were interviewed about the languages spoken in their families. One has to support multilingualism of the migrant children. Baur demonstrates interesting results of the SPREEG survey, for example that there are migrant children in all (!) primary schools in Essen. The SPREEG-survey helps to detect deficiencies in school policies. One of the most important topics discussed in the paper is the core area of DaZ: teacher training. In 2009 parts of the DaZ program (curriculum) became compulsory for all candidates taking a teaching degree. A DaZ-module was developed and made available to other universities. The Project ProDaZ was granted by the Mercator Foundation. To conclude, the author deals with an important topic – the relationship between theory and practice in teacher education. The author mentions the main projects at the University Duisburg-Essen, which contribute to the benefit of the students: – remedial teaching (Förderunterricht) for children and adolescents with migrant backgrounds – the project “Language through Art” (museum visits in order to get in contact with art, learn how to express the perception of art through language, also for children with migrant backgrounds) – design and development of C-Tests There are also some projects in the DaF area: – cooperation with the University of Saratow (Russia) for the integration of Russian-German emigrants – reconstruction of the German Studies at the University of Kabul, Afghanistan.