Theophylline has been used in the treatment of obstructive pulmonary diseases since 30s. However, its mechanism of action is still poorly defined. Up to now, its several different actions on the cellular levels are known or hypothesised including most important ? inhibition of phosphodiesterase isoenzymes and antagonism of adenosine, as well as enhancement of catecholamine secretion and modulation of calcium ions fluxes. Author reviews all of the proposed theories, outlining existing arguments for and against.