Evidence suggests that involving patients in health care decisions has a positive impact on health care outcomes and patients' perception of quality. However, the extent to which dental students are trained in communication and shared decision making (SDM) differs, and studies have identified a need for intensified learning and assessment of this competence. A need to more clearly define and operationalize what it means to be proficient in this area has been identified. The aim of this study was to operationalize communicative and relational skills in a comprehensive assessment instrument for SDM. Relevant skills in information exchange, negotiation, communication, and relationship-building were identified through an extensive review of previous research and instruments for assessing communication competence. Indicators for assessing these skills were formulated. The instrument was submitted to a pilot test in 2016 and evaluated on test content, internal structure, and response processes. The Assessment of Shared Decision Making (ASDM) instrument consists of 18 items addressing various aspects of the construct and three types of skills. Findings suggest that the ASDM represents a valid measure of SDM with three major components. The importance of developing the ASDM lies both in the summative assessment of students' communication with patients and for formative assessment purposes. Once identified, the components essential for SDM can be woven into the curriculum and shared with students. Thus, the ASDM provides a structure that can meet the need for intensified learning and assessment of dental students' competence in communication and SDM.