History
In 1970, the Association of Tennis Professionals inaugurated its Masters Tournament as a round-robin championship event involving the top eight players from the season's tour.
The format was revised in 1972 to begin with round-robin competition determining the four semi-finalists, who were then seeded by their round-robin finishes. The Masters went to straight single-elimination format in 1973.
There was no tournament in 1977, because the event was moved from December to January. In 1986, it moved back to December, so there were two tournaments that year.
From 1978 through 1989, the Masters was staged in Madison Square Garden. It was renamed the ATP Tour World Championship in 1990 and has been played in Frankfurt, Germany, since then.