It has been recognised for some considerable time that contraction of airway smooth muscle is largely responsible for the bronchospasm that is a characteristic feature of the acute phase of an asthmatic attack. It is also well accepted that airway smooth muscle of asthmatic subjects is hyperresponsive to a wide range of provoking stimuli. One might anticipate, therefore, that a substantial amount would be known about the physiological role of airway smooth muscle. Surprisingly, this is not the case. The purpose of this article, therefore, is to provide an overview of airway smooth muscle with special reference to contractile mechanisms since they are, clearly, of relevance in asthma. In addressing this remit the following subject matter has been covered--structural aspects of the airway smooth muscle cell, electrical and calcium ion channel characteristics of the cell membrane, signal transduction mechanisms in relation to excitation-contraction coupling and the biochemical basis of contraction.