Poor inhaler technique impairs the delivery of medications in patients with asthma and COPD. Recommendations in asthma and COPD guidelines presuppose that healthcare professionals have the knowledge and tools to select inhaler devices appropriate for individual patients. Appropriate selection or personalization and correct use of inhaler devices are integral components in the management of asthma and COPD. It is well known that there are many challenges with the use of inhalers, and no one device suits all patients. The present lecture includes the science and principles behind commonly used inhalers in asthma and COPD, such as pressurized metered dose inhalers (pMDIs), dry powder inhalers (DPIs) and soft mist inhalers (SMIs). The lecture highlights the importance of effectively matching inhaler devices to individual patients' needs and abilities in treatment decisions. The role of pharmacists in optimizing inhaler devices through the Respiratory Medication Therapy Adherence Clinic (RMTAC) is also included in the present lecture.