Asthma and chronic obstructive pulmonary disease (COPD) are highly prevalent chronic diseases in the general population. Both are characterized by similar mechanisms: airway inflammation, airway obstruction, and airway hyperresponsiveness. However, the distinction between the two obstructive diseases is not always clear. Multiple epidemiological studies demonstrate that in elderly people with obstructive airway disease, as many as half or more may have overlapping diagnoses of asthma and COPD. A COPD-Asthma overlap syndrome is defined as an airflow obstruction that is not completely reversible, accompanied by symptoms and signs of increased obstruction reversibility. For the clinical identification of overlap syndrome COPD-Asthma Spanish guidelines proposed six diagnostic criteria. The major criteria include very positive bronchodilator test [increase in forced expiratory volume in one second (FEV1) ≥15% and ≥400 ml], eosinophilia in sputum, and personal history of asthma. The minor criteria include high total IgE, personal history of atopy and positive bronchodilator test (increase in FEV1 ≥12% and ≥200 ml) on two or more occasions. The overlap syndrome COPD-Asthma is associated with enhanced response to inhaled corticosteroids due to the predominance of eosinophilic bronchial inflammation.The future clinical studies and multicenter clinical trials should lead to the investigation of disease mechanisms and simultaneous development of the novel treatment.