Orally inhaled products delivered via inhalation exert their effect directly to the target organ. This allows to administer a very low dose of a drug compared with an oral route with similar clinical effect and significantly reduced toxicity. However inhalation therapy is also limited by several factors. Delivery of the desired dose of the drug to the airways depends on a type of the inhaler - pressurised metered-dose inhaler (pMDI) or dry powder inhaler (DPI), inhaler characteristics (low or high internal resistance, diameter of particles and distribution of the generated aerosol fine particles), thermal conditions of air, and ability of patient to generate sufficient inspiratory flow (for DPI) or to coordinate actuation with inhalation (for pMDI). Unlike pMDIs, DPIs are breath- -actuated, hence avoiding the need for the patient to coordinate actuation with inspiration. Furthermore, DPIs are propellant-free and do not produce the cold sensation on inhalation. Currently available DPIs vary widely in design, operating characteristics and performance. And poor inhalation technique may compromise treatment efficacy. Hence, there is a clear need for a careful selection of DPIs for different patient groups, including children, elderly patients and those with severe airway obstruction.