This paper is concerned with the synchrotrons and storage rings which accelerate protons and electrons for high energy physics. First we trace the development of these machines from early cyclotrons, pausing to describe the main principles of their operation as they emerge. After briefly introducing the reader to the present generation of synchrotrons, we explain in more detail how such large machines are designed, drawing together a consistent whole from a diversity of technical components. We make no attempt to describe the construction phase but move to the running in where component systems must be made to work together and design principles are put to the test.