Jessica Ennis-Hill and Katarina Johnson-Thompson get underway at the Olympic Games on Friday.
Great Britain's star heptathletes will be in action as the athletics makes it long-awaited debut at Rio 2016, kicking off the first of their seven events.
Reigning gold medallist Ennis-Hill and team-mate Johnson-Thompson, who is expected to vie for the top honours this time around, take part in the 100m hurdles.
Brit watch
Bradley Wiggins takes centre stage as the cycling team pursuits begin at Rio's Velodrome. The champions from London 2012 are comprised of Wiggins, Ed Clancy, Steven Burke, Mark Cavendish and Owain Doull.
Charlotte Dujardin will be hoping to lead Great Britain into dressage's grand prix special - a team event won by the hosts at London 2012. Dujardin, riding Velagro, teams with Spencer Wilton, Carl Hester and Fiona Bigwood but 2014 world champions Germany have an eye on gold, too.
Jo Pavey, in her fifth consecutive Olympics, opposes team-mates Beth Potter and Jess Andrews in the women's 10,000m final. In the hockey, Great Britain's men play Spain.
Going for gold
Michael Phelps and his biggest rival Chad le Clos could come head-to-head once again if they both make Friday's swimming (100m butterfly) final, as expected. Their feud has already emerged as one of Rio 2016's biggest talking points after Phelps beat Le Clos in the 200m butterfly to claim his 21st career Olympic gold. The tension beforehand was palpable.
Katie Ledecky aims to continue her swimming dominance in the final of the 800m freestyle, her favourite event. The American is just 19-years-old but has already picked up three golds in Rio, to add to the prize she won at London 2012.
Don't miss
The women's shotput. Valerie Adams bids for unique history having already won gold in Beijing and London. The dominant New Zealander leads the field in Friday's qualifier before Saturday's final.