Volleyball was introduced to the Olympics for both men and women in 1964. It is played by teams of six on an indoor court measuring 18m x 9m, with a net 2.43m high for men and 2.24m high for women.
Each team is allowed to touch the ball three times before it has to cross the net. The object is to make the ball hit the ground in your opponent's half of the court, or to make your opponent hit the ball out.
Typically the players will use the first and second touches to set up an attempt to score by hitting the ball powerfully to try and ground it in the opponent's half of the court — a move known as "set and spike". No player can touch the ball twice in succession.
Each team features a libero who wears a different-coloured shirt. While other players are obliged to rotate their position between points, the libero remains in a central position at the back of the court.
He or she does not serve, and is not allowed to spike the ball when it is above net height.
Matches are played in a best-of-five sets format. 25 points are needed to win the first four sets (with a margin of two), and 15 to win the fifth set.
The men's and women's events in London will each feature 12 teams and will begin with a preliminary round-robin tournament in two pools of six. The eight best teams will then progress to the knockout phase.
The Soviet Union won the first two men's tournaments and took gold again in 1980, but they have collected only silver and bronze as Russia since then. The United States triumphed in 2008 to take their total to three golds, while Brazil have been champions twice since 1992.
The women's event brought a hat-trick of golds for Cuba from 1992 to 2000, but the Soviet Union claimed four events between 1968 and 1988, while Russia picked up silvers in 2000 and 2004.
Beach volleyball, which was added to the Games schedule in 1996, is a pairs competition played outdoors on a court covered in sand and measuring 16m x 8m.
In London the men's and women's events will each feature 24 teams in six pools of four, with 16 progressing to the knockout phase.
The United States were denied a clean sweep of men's beach volleyball golds by Brazil's victory in 2004, while the Americans have carried off the women's event twice, with Brazil taking gold in 1996 and Australia in 2000.