Coding schemas are a central part of qualitative research in methods like Grounded Theory and Qualitative Content Analysis. Therefore, coding schemas play an important role in order to make research with these methods more transparent in the sense of Open Science. This doctoral dissertation presents the ontology QualiCO, a formal description of coding schemas. As part of the development, first a requirements analysis was conducted using stakeholder analysis, participant observation, expert interviews (n=10), and analysis of previously published category systems and textbooks of Grounded Theory and Qualitative Content Analysis. Based on this, a development phase followed. In this case, a participatory design was chosen with the evaluation of paper prototypes (n=5), an evaluation of a prototype platform of the ontology (n=4) as well as the presentation of QualiCO at different workshops. At the end of the research process, the ontology was evaluated with the help of a qualitative usability test (n=20) and a metrics-oriented qualitative evaluation (n=10). As interview partners, researchers from German-speaking qualitative educational research who already had experience with the aforementioned methods were recruited. For the usability tests, researchers from Human-Centered Design at the University of Washington in Seattle were selected. Although QualiCO was developed with German-speaking educational researchers in mind, it also met the requirements of the evaluation with researchers from Human-Centered Design. It can probably be used by other research communities working with Grounded Theory or Qualitative Content Analysis. The dissertation also describes the working methods of researchers in the field of Grounded Theory and Qualitative Content Analysis and shows the following potentials for the ontology: Publication of coding schemas, validation of coding schemas, identification of inspiration for researchers, visualization of relationships between codes, usefulness of ontology in teamwork, description of coding ...