The National Institute of Standards and Technology (NIST) provides its Internet Time Service (ITS) to the general public. The service distributes Coordinated Universal Time (UTC) kept at NIST and called UTC(NIST), which is an official source of time both in the United States and internationally. The ITS is an important part of the nation's timekeeping infrastructure. Primarily used for the synchronization of computer clocks, the service currently (2001) handles hundreds of millions of timing requests per day. This chapter describes the ITS in detail. It provides a physical and technical description of the service, and explains how NIST provides and maintains the ITS for the American public.