Adherence to therapy plays a key role in treatment optimization and clinical outcome in patients with chronic obstructive pulmonary disease (COPD). The adherence to inhaled medications is poor, ranging from 20% to 60%. In this study we searched Medline and PubMed literature regarding factors that could have an impact on therapy adherence in COPD patients, using the key words "COPD" or "chronic obstructive pulmonary disease" and "adherence". The search was limited to the English language article published between January 2013 and December 2019. Review papers, study protocols, and meta-analyses were excluded. The final material included 25 articles. The evaluation was performed using the Cochrane Review Manager guidelines. The 25 articles represented 29 countries from 5 continents. We assessed adherence to therapy and the impact of selected factors on the adherence in 27,660 COPD patients (60.9% of whom were male, mean age 64 years). The factors affecting adherence were broken down into three categories: sociodemographic, clinical, and psychological. There were two standardized instruments used in the analyzed studies: Test of Adherence to Inhalers (TAI) and self-reported Morisky Medication Adherence Scale (MMAS-8). We found that 46.3% of patients had a moderately good level of adherence to inhaled therapy (TAI range around 50 points), while 41.6% of patients had a high level of adherence to oral therapy. The nature of non-adherence was in most cases inadvertent rather than an erratic or deliberate demeanor (48.5% vs. 38.9% vs. 42.4%, respectively). We conclude that standardized instruments enable the prediction of adherence to therapy and should be used in clinical practice. The assessment of adherence is essential for undertaking interventions to counteract plausible non-adherence. Collaboration between an educator and a psychologist is required to evaluate the patient's motivation and to ensure his comprehension of treatment prescribed.