Precise timekeeping and navigation systems have a lot in common. Both are based on ultraprecise atomic clocks, on the capacity to measure and synchronise clocks and on the formation of a common reference time traceable to international standard time. These similarities are described, showing how time and frequency metrology has found a major application in navigation systems, and how the pressing needs of navigation have promoted research in time metrology fields. The paper focuses on the clock and navigation equations, the necessary algorithms, and the definition of time scales used as a reference in navigation and in timekeeping.