Medication non-adherence is a global problem that has been studied over the past 40 years. Despite the large number of studies there is not an agreed upon definition of “adherence” in the literature. The lack of a consistent definition has resulted in issues in adherence research, clinical implementation, and HIT system development. In this paper a critical review of adherence literature is conducted. Based on this review, a new Adherence Interaction Model (AIM) is proposed and described in detail. AIM considers provider recommendations, the patient's interpretation of the recommendations, and the patient's behavior and provides the foundation for building a more objective view of adherence. AIM provides a foundation for future formalization of medication adherence concepts.