Objective: Physical activity and healthy nutrition can reduce the progression of type 2 diabetes mellitus and coronary heart disease. Accordingly, copious interventions to increase such behavior have already been presented. However, such interventions are usually poorly described and there has not been much public scientific Discussion regarding their theoretical derivation. To promote such a Discussion, the theoretical derivation of a telephone-based health coaching (TBHC) intervention for patients with type 2 diabetes and coronary heart disease and the resulting intervention are presented. Methods: The intervention is conceived as a combination of (1) the interaction between coaches and patients and (2) measures to ensure the quality of this interaction. The interaction between coaches and patients consists of (1) the style and (2) the contents of this interaction. The style of the coach-patient interaction is derived from Self-Determination-Theory and concretized using Motivational Interviewing techniques. The contents of the coach-patient interaction are derived from the Health Action Process Approach and concretized using Behavior Change Techniques. Results: Material for guiding the coach-patient interaction has been produced. This material consists of 16 tools to be applied in the coaching sessions and guidelines for selecting the appropriate tool for each session. The quality assurance measures consist of a coach training program before and supervision sessions during the TBHC. Conclusions: The theoretical derivation yielded an operable intervention. Both the process of derivation and the resulting intervention could prove useful for researchers designing similar interventions. The project upon which this abstract is based was funded by the Innovation Fund of the Federal Joint Committee under the funding code 01NVF18033.