Nonadherence to treatment, and its associated health and economic burden, is particularly problematic in asthma and chronic obstructive pulmonary disease management because of heterogeneous patient populations and the need for an inhaled route of drug administration. Symptom variability, comorbidities, and device switching further add to suboptimal adherence rates. As opposed to controlled clinical trials, real-life studies show consistently low inhaler adherence in daily practice, yet exact adherence rates have long been affected by disagreement on standardized definitions. The recently developed Ascertaining Barriers to Compliance taxonomy helps to address adherence research disparities by identifying 3 phases of adherence (initiation, implementation [including correct inhaler technique], and discontinuation). This review considers the reasons for and impact of suboptimal adherence, together with summaries of key studies that demonstrate how improving adherence can reduce exacerbations, inhaled corticosteroid use (in cases of better inhaler technique), hospitalizations, and treatment costs. Strategies to help ensure optimal adherence are discussed, including the choice of a patient-tailored inhaler, patient empowerment, education and training, and the potential of electronic monitoring and digital technology. It is concluded that a combined effort from payers, health care professionals, and manufacturers could make a real difference to asthma and chronic obstructive pulmonary disease control, as well as to health care budgets.