Applications of clocks and frequency standards: from the routine to tests of fundamental models

The traditional applications of clocks and oscillators in navigation and scientific research continue to grow as new and more widespread applications emerge. Today, clocks and oscillators regulate the speed and efficiency of virtually every human endeavour ranging from the mundane to the exotic. In this paper we discuss some of the applications that require the service of high performance clocks and oscillators. In particular, we discuss space applications of clocks for navigation and scientific experiments. We also present a discussion of satellite navigation systems, especially the Global Positioning System, and comment on time dissemination over the Internet.