This book speaks to the technological infrastructure of time dissemination, distribution, and synchronization, specifically the architecture, protocols, and algorithms of the Network Time Protocol (NTP). NTP has been active in one form or another for over almost three decades on the public Internet and numerous private networks on the nether side of firewalls. Just about everything today that can be connected to a network wire has support for NTP: print servers, WI-FI access points, routers and printers of every stripe, and even battery backup systems. NTP subnets are in space, on the seabed, onboard warships, and on every continent, including Antarctica. NTP comes with most flavors of Windows as well as all flavors of Unix. About 25 million clients implode on the NTP time servers at the National Institute of Standards and Technology (NIST) alone (J. Levine, NIST, personal communication).