Present research regarding interventions to change behavior suffers from insufficient communication of their theoretical derivation. This insufficient communication is caused by the restrictions imposed by most of the relevant scientific journals. This impedes further intervention development. In this article, a telephone-based health coaching (TBHC) intervention is introduced using a format outside these restrictions. This intervention is seen as a combination of (1) the activities performed with the target persons, i.e., its core, and (2) measures to ensure the quality of the intervention. The theoretical derivation of the core is presented. The core is seen to consist of (1) the style of coach–patient interaction and (2) the contents of this interaction. The style of coach–patient interaction was derived from self-determination theory and was concretized using motivational interviewing techniques. The contents of the coach–patient interaction were derived from the health action process approach and were concretized using behavior-change techniques. The derivation led to (1) a set of 16 coaching tools referring to the different states in which a patient might be and containing state-specific recommendations for performing the coaching session, and (2) guidelines for selecting the appropriate coaching tool for each session. To ensure the quality of the intervention, a coach-training program before and supervision sessions during the TBHC were added.