The Tennis Masters Series rebranded this year as the ATP World Tour Masters 1000 is the latest incarnation of a series of sub-Grand Slam tournaments designed to attract all the biggest players in the game.

However, after a number of years in which top stars have chosen to miss certain of the so-called elite events, the ATP announced significant changes for the 2009 season, making eight of their new 1000 tournaments mandatory.

The major events were scheduled to take place in Indian Wells, Miami, Monte Carlo, Rome, Madrid, Toronto/Montreal, Cincinnati, Shanghai and Paris although entry in Monte Carlo was not mandatory.

In addition, the season-ending ATP World Tour finals were moved to the O2 Arena in London after being staged for the previous four years in Shanghai.

The move to make tournaments mandatory was not universally popular among some leading players, who protested about the rigours of the tennis calendar.

In addition, the original decision to leave Monte Carlo out of the final nine was heavily criticised and led to a lawsuit by the tournament's officials, which resulted in its reinstatement, albeit not as one of the mandatory events.

Since the series was introduced as the Tennis Masters Series in 1990, Andre Agassi leads the way with 17 title wins, including six triumphs in Miami, although his record is coming under increasing threat from Roger Federer and Rafael Nadal.

Tim Henman won his only Tennis Masters Series title in Paris in 2003, but Andy Murray has already won three, in Cincinnati and Madrid in 2008, and this year in Miami.