"O" is Cirque du Soleil's permanent show at the Bellagio Hotel and Casino. The title is a play on the French word for water = "eau".

Cirque de Soleil weaves a legacy of homage to the magical nature of theater in "O", the aquatic production. Inspired by the concept of infinity and the elegance of water's pure form, "O" demonstrates that anything is possible. The production's centerpiece and recurring element is the massive pool, which holds more than 1.5 million gallons of water and reaches a depth of 25 feet. The dimensions of the pool are 150 x 100 feet at the widest point. The water is cycled through a complex filtering system which takes six hours for all 1.5 million gallons to pass through. The pool temperature is kept at 80 degrees. The pool takes approximately 12 hours to fill and is drained annually for maintenance. The water can be drained into the 22 million gallon lake in front of the Bellagio and raises the water level one inch.

The music draws from the talents and background of musicians around the world and blends them into teh aquatic realm of "O". The score was composed by Benoit Jutras and is performed by 10 live musicians from Canada, Senegal, China and the United States. The band for "O" utilizes a very unique combination of instruments, including a cello, Colombian guitar, African harp, bagpipes, Chinese violin, ancient woodwinds and a wide variety of percussion instruments.

The production includes synchronized swimming, high diving trapeze and contortion.