In tennis, the ATP Masters 1000 events, often shortened to Masters 1000 or ATP 1000, are an annual series of nine top-level tournaments featuring the elite men's players on the ATP Tour since 1990. The ATP 1000 tournaments along with the Grand Slam tournaments and the year-end championships make up the most coveted titles on the annual ATP Tour calendar. In addition to the quadrennial Olympics, they are collectively known as the 'Big Titles'.