Most clinicians are interested primarily in the pathogenesis and pathophysiology of those disease processes that affect the organ system with which their specialty is concerned. Accordingly, the structure of this book is such that the specialist can focus attention on the anatomy, physiology, disease mechanisms, and investigative models in the microcirculation relevant to his or her discipline. However, as will be apparent from the Contents pages of this book, malfunction of the microcirculation is a feature of many disease states; and without a framework for thinking, it is difficult to build detailed organ-specific knowledge. The purpose of this chapter is to help create such a framework.