In American football, there are generally four quarters consisting of 15 minutes of game time each, with possible extra overtime quarters. This structure is used in most high school, college and professional leagues.
There is usually a small break at the end of the first and third quarters as teams change sides on the field, and a longer "halftime" break in between the second and third quarters. If the score is tied at the end of regulation time, at least one overtime quarter is played. In the NFL, if the game remains tied at the end of overtime, the game ends in a tie unless it is a playoff game or the Super Bowl, in which case overtime quarters continue indefinitely until a team wins the game.