Adherence broadly encompasses the decisions patients make as to whether health care advice should be initiated, as well as the degree to which the recommended health behaviors, once started, are maintained. Disease-related conditions such as severity and duration of illness, as well as treatment-related features such as frequency of dosing and side effects, are 2 of several factors that influence adherence. Other factors affecting adherence include socioeconomic status, patient-related causes, and health system-related reasons. Adherence is rarely, if ever, an all-or-none phenomenon. Typically, patients follow some recommendations closely while deciding others are optional; these decisions are often made without consulting with or notifying health care professionals. Non-adherence can be categorized as either unintentional or intentional. Unintentional non-adherence is easier to remedy because it responds to patient education, simplification of treatment regimens, or the use of a reminder system. Intentional non-adherence is more complex and challenging to address because patients exhibiting these behaviors often do not find evidence-based recommendations compelling, lack the motivation to follow advice, or have deeply entrenched personal beliefs that conflict with health guidance. Novel psychotherapeutic behavioral interventions, such as shared decision-making, motivational interviewing, and coaching are some approaches being tested to determine their effectiveness in mitigating the resistance to treatment that characterizes intentional non-adherence in asthma and COPD populations. In this narrative review, the extent of non-adherence to asthma and COPD management recommendations is explored, the factors affecting adherence are explicated, the methods used to measure adherence are compared and contrasted, and the effectiveness of strategies targeting unintentional and intentional non-adherence is detailed.