This is an introductory text designed primarily for students of medicine and physiology. The author shows how knowledge of the circulation is derived from experimental observations. Human data are presented where possible, and their relevance to human disease is emphasized. The traditional weighting of subject matter has been re-thought, resulting in a fuller account of microvascular physiology. This reflects the explosion of microvascular research over the last two decades. Even setting aside these advances, it seems self-evident that the culminating, fundamental function of the cardiovascular system, the transfer of nutrients from plasma to the tissue, merits more than the half-a-dozen lines usually accorded to it in introductory texts. Major advances continue apace in other fields too, for example the elucidation of the biochemical events underlying Starling's law of the heart; the discovery of new vasoactive substances produced by endothelium: the exploration of non-adrenergic, non-cholinergic neurotransmission; rapid advances in vascular smooth muscle physiology; and new concepts of how the central nervous control of the circulation is organized.