There are 3 periods. Each period lasts 20 minutes (of actual playing time). If you have a tie at the end of the third period, then an overtime period (or sometimes even 2 or 3 overtime periods) must be played until someone scores a goal, thus ending the game. If no one ever succeeds in scoring another goal, overtime periods must continue being played until..................umm......well, for a pretty damn long time, eh?

;-)

That's as best I can remember it. I never played hockey myself, cos I grew up mostly in New York State, not Canada, and hockey wasn't big where I was living. The games that were big around there were football, basketball, and baseball.