There is an absence of empirically based standards for pre-service teacher education regarding competencies in the field of German as a Second Language (GSL) needed for being able to adequately facilitate second language learners in the mainstream classroom. The DaZKom study aims to fill this gap by providing a theoretical framework and competency model in this field for pre-service teachers of all subjects. This article primarily focuses on the rationale, generation, and explication of the GSL competency model, which discerns three dimensions: subject-specific registers, multilingualism, and didactics. The model also describes three competency stages, which are based on the first three stages of the Five-Stage Model of Adult Skill Acquisition by Dreyfus & Dreyfus (1986). In order to empirically measure preservice teachers’ GSL competencies, a paper and pencil test was developed on the basis of the model and tested on a large sample of pre-service teachers; the model was further content validated by a group of experts from the field of GSL and educational science.