The American swimmer Michael Phelps is attempting to break his compatriot Mark Spitz's record of seven gold medals at an Olympics. The 23-year-old from Baltimore begins his quest in the 400m individual medley. The heats begin today at 11.30 and the final is at 03.00 tomorrow morning.
Craig Fallon, right, could become Britain's first gold medal winner of the Games when he competes in the judo extra lightweight competition (the final is at approximately 11am today). The 25-year-old from Wolverhampton, who was knocked out in the second round four years ago, is the first British man for 25 years to hold the world and European titles at the same time.
Several British crews start their campaigns in the rowing competition, including the men's four, who have won gold at the past two Games (heats at 10.30am today).
Bradley Saunders, one of Britain's best prospects for a boxing gold, starts his light-welterweight campaign against Neequaye Samuel Kotey (13.00 tomorrow)
Cyclists Nicole Cooke and Emma Pooley both have medal chances in the women's road race (starts at 7am tomorrow and likely to finish at about 10am).
Best of the rest
What you may have missed overnight...
05.00 Archery: Britain's Alison Williamson (above), a contender for the podium, took part in the individual round.
06.00 Sailing: Ben Ainslie, racing in the Finn class, began his attempt to win a third Olympic gold medal. He has three other races in the Finn class this weekend (07.00 today, 06.00 and 07.00 tomorrow).
COMING UP LATER TODAY
10.00 (approx) Cycling: Finish of the men's road race, featuring the last two Tour de France winners, Carlos Sastre and Alberto Contador.
12.45 Women's football: China take on Canada.
03.30 Tennis: First day's play, featuring matches in all four competitions.
12.45 Swimming: Britain's Liam Tancock, 50m backstroke world-record holder, competes in the 100m backstroke heats.
13.05 Swimming: First round of 400m freestyle heats, in which Britain's Rebecca Adlington is a possible medallist
15.15 Men's basketball: China, led by the Houston Rockets' Yao Ming, take on the United States in their first match.
All times BST
The weekend will be hot (28C) with a chance of thunderstorms tomorrow.