In this chapter, we examine the vasculature and how blood flows round the body. We then introduce the study of blood flow and how it can be modelled using very simple techniques, using the equivalent electrical circuit as an example. Then we examine how techniques from Chap. 6 can be employed to model individual vessels and the propagation of pulse waves from the cardiac cycle. We will also look at how blood pressure and blood flow is measured and these are controlled to maintain adequate supply to the body.