Tennis Masters Series
(ATP "Super 9" or
Mercedes Super Nine)

The tournaments on the ATP tour are designated into two main tiers (excluding Challenger events), called Championship Series and World Series.   Championship series events offer more prize money and attract bigger-name players.

The ATP has given special status to 9 of their Championship Series tournaments.  These tournaments are known as the Tennis Masters Series. All of them have changed their names to the words "Tennis Masters Series" followed by the name of the city closest to the event (all except Miami which had a prior committment to Ericsson when the change was announced in December, 1999).

An ATP Top Ten player is supposed to play in at least 8 of these 9 special events, and each event must field at least eight of the Top Ten men (singles).   The idea is to get the top players to play each other more often and add prestige to selected ATP events.

A rule change in 2000 states that all players ranked high enough to enter must play in all of these 9 Tennis Masters Series events as well as the four Grand Slams. These 13 events, therefore, now constitute the "major" events in men's tennis. If a player doesn't play in one of these events for whatever reason he loses money in the bonus pool, and he gets zero points added to his ranking for that event (which he cannot make up for by doing well at another non-major event). 
For example, not playing Wimbledon cannot be compensated for in the points race by winning Indianapolis. The idea is that the public should be able to expect some events (those which are most important to the sport) to have all of the top players.