A standard ice hockey game has three periods. In professional hockey, each regulation period lasts 20 minutes of playing time, producing 60 minutes of regulation action.
The clock stops whenever play is interrupted, so a 60-minute game usually takes much longer in real time. Between the periods, players leave the ice for intermissions, and teams change ends after each period. This arrangement helps balance factors such as ice conditions and the effects of the arena environment.
If the score is tied after regulation, the game may continue into overtime. NHL regular-season games use a short sudden-death overtime followed, if necessary, by a shootout, while playoff games continue with additional sudden-death periods until someone scores. Those extra sessions do not change the number of regulation periods: the standard game still consists of three.
Youth and recreational leagues may shorten the length of each period, but they commonly retain the three-period structure.