With the advent of numerous technologies that allow for the stabilization and measurement of optical frequencies, atomic clocks have progressed rapidly towards new levels of stability and systematic uncertainty. Progress in laser cooling, atom trapping and state detection has led to a diversity of atomic systems that are now amenable for use as high-accuracy frequency references. At the same time the breadth of the scientific and technological applications of these frequency measurements has increased.
In this tutorial I will provide an overview of the principles of optical atomic clocks, the technologies that make them possible and the applications that motivate their development. I will survey some recent developments in the field that I hope will put some of the new results we hear about during the conference in context.