Aerosol inhalation is considered the optimal route for administering the majority of drugs for the treatment of obstructive airways diseases. A number of Pressurised Metered-Dose and Dry Powder Inhalers are available for this purpose. However, inhalation of therapeutic aerosols is not without difficulty; it requires precise instructions on the inhalation manoeuvre, which is different from spontaneous normal breathing. Also, the characteristics of the inhaler device have to be suitable for the user. Available data indicate a frequent lack of knowledge demonstrated by health professionals and patients on the inhalation manoeuvre and handling of inhalers, resulting in a reduction of therapeutic benefit. This paper reviews the literature concerning the fundamental aspects of inhaler devices, inhalation manoeuvre and device selection, in an attempt to increase the knowledge of, and to optimise the clinical use of, therapeutic inhalers.