Precision timing of pulses is at the heart of pulsar research. Pulse arrival times can be measured to an accuracy of only a few metres travel time, and analysis must take account of pulsar positions and the Earth’s orbit, the Römer correction to the barycentre, and General Relativistic corrections. Pulsar timing contributes to the comparison of fundamental positional reference frames. Timing provides periods and period changes on short and long time scales, giving pulsar ages and proper motions. The precision timing of some millisecond pulsars is comparable to the best terrestrial laboratory clocks.