Since the 1994-95 season, clubs have received three points for a victory, one point for a tie, and no points for a defeat. The team that has most points at the end of the season is declared champion.
Before then, there was only ever one Serie A winner. This changed with the creation of UEFA's European Champions League in 1955. Juventus were undefeated champions in both seasons it operated (1955-56 and 1957-58). However, because UEFA rules stated that only one club could be crowned champion per year, Bologna were given the title instead. They went on to win the championship the following two seasons as well.
There have been several attempts to create a double or treble winning season but they have all failed. In 1995-96, Vicenza and Reggiana ended up tied on points at the end of the season - since then, neither can claim the title.
In 2004-05, Milan finished with 100 points but due to financial irregularities had their record expunged. They would have won the title anyway because they had a better goal difference than Roma but the latter's title win was later confirmed by default as Milan had already left the league.
In 2009-10, nine points separated first place from last in the table.
A victory is worth three points, a draw is for one point, and a defeat is worth none, with the side with the most points at the conclusion of the season claiming the Premier League championship. The winner of the English Football League Championship wins the second place prize while the third-place finisher claims the third spot.
In the Premier League, each team plays every other team twice, once at home and once away, for a total of 38 games per season. Teams have up to October 31 to decide how they want to finish their season - either by trying to gain advantage in the league table or by attempting to achieve a top-three position and secure a place in next year's Champions League tournament.
The winner of the Premier League is based on final standings between teams after these two phases are complete. If two or more teams are equal on points, the ranking will be determined by goal difference in its entirety first, then goals scored will take priority over goal difference. If still tied, it will be decided by a penalty shoot-out (same as in tennis).
In addition to the title, the Premier League awards several other prizes.
There are three points. It is possible for two or more teams to have the same number of points at the end of the season - this has happened twice before - so it is possible for there to be no champion until the last weekend of the season.
It is also possible for only one team to have any points at all. In this case, the winner of the league would be determined by which team scored the most goals during the season. This would be called "goals scored" rather than "points won".
In the current Premier League season, which began on August 13, 2012 and will end on May 17, 2013, Manchester United are first with 51 points, followed by Chelsea with 48 points. Tottenham Hotspur and Liverpool are third and fourth respectively with 47 points.
It's possible to win the Premier League without scoring any goals if your opponent fails to score any either. For example, if Manchester United beat Newcastle United 3-0 while Newcastle fail to score anywhere near enough goals to be considered winners, then Manchester United would claim their sixth championship in history.