Anatomically, the lung is characterised by a dual blood supply. The existence of a systemic bronchial arterial supply to the lung in addition to the pulmonary arteries was first described by Galen in the second century. From angiographic studies it is known that pulmonary lesions of different aetiologies are characterised by differences in arterial supply. Colour Doppler sonography makes it possible to classify pulmonary arteries by location, flow direction, and quantitative spectral curve analysis. This article will review pathophysiological and colour Doppler sonographic basics of pulmonary vascularity.