  Time plays a crucial role in the intuitive understanding of the world around
us. Within quantum mechanics, however, time is not usually treated as an
observable quantity; it enters merely as a parameter in the laws of motion of
physical systems. Here we take an operational approach to time. Towards this
goal we consider quantum clocks, i.e., quantum systems that generate an
observable time scale. We then study the quality of quantum clocks in terms of
their ability to stay synchronised. To quantify this, we introduce the
"Alternate Ticks Game" and analyse a few strategies pertinent to this game.
