Introduction: Adherence to treatment is one of the most important issues in the field of physical and mental illnesses that have received little attention in Iran. Many patients do not adhere to treatment and ignore the doctor's instructions, which this is associated with economic, physical, and cultural problems for the individual, family, and community. The purpose of this study was to investigate the theoretical and practical dimensions of adherence to treatment in the health care system. Materials and Methods: This is a descriptive-analytical study. Articles related to theoretical and research literature on adherence to treatment were searched in the databases of Scholar Google, Nursing index, Elsevier, Scopus, and also the related books. Articles were searched from 1990 to 2019 using the keywords of adherence to treatment and the patient, and theories and models were combined. Results: The results of various studies showed that non-adherence to treatment in many disorders can cause irreparable damage. Anderson's behavioral model and common sense model are models of treatment adherence that can have therapeutic and practical uses. Children, the elderly, and patients with psychological problems are among the groups with low adherence to treatment. Conclusion: Based on the results, physicians and specialists should help patients to improve their adherence to treatment by applying and adhering models in this context, as neglecting this phenomenon will have many negative individual and social consequences especially in some groups.