LONDON (CNN) -- Some of the fastest men and women in the world are preparing Wednesday to go for gold in the Olympic Stadium, with American medal hopes high in the women's 200-meter final and the men's 110-meter hurdles.
Veronica Campbell-Brown of Jamaica has won the past two Olympic 200 meters for women but was beaten at her national trials by Shelly-Ann Fraser-Pryce, who won the 100 meters gold on Saturday.
They'll be keeping an eye on Allyson Felix of the United States, who ran the fastest time in the past 14 years in winning the U.S. trials and is a favorite for gold in the 200-meters. Fellow U.S. sprinters Carmelita Jeter and 400-meter winner Sanya Richards-Ross also have medal hopes.
Americans Lashinda Demus and T'erea Brown are among those to watch in the women's 400-meter hurdles final.
There is a guaranteed gold for Team USA in the women's beach volleyball final at historic Horse Guards Parade, as two American pairs get set to battle it out on the sand.
Defending champions Misty May-Treanor and Kerri Walsh Jennings will be looking to make it three Olympic golds in a row, but April Ross and Jennifer Kessy will be doing their best to claim the top honor themselves.
There are 16 gold medals up for grabs in eight different sports on day 12 of the London Games.
The men's decathlon got going Wednesday, with athletes taking part in the 100-meters, long jump and shot put. Team USA's Ashton Eaton and Trey Hardee were in first and second place after the first three events.
The women's 800-meter heats got under way Wednesday, with defending champion Pamela Jelimo of Kenya the fastest winner of her heat. Team GB's Lynsey Sharp qualified close behind her.
Caster Semanya, the South African athlete who was the subject of a gender test by the International Association of Athletics Federations following her victory in Berlin at the world championships three years ago, also qualified as the second-fastest finisher in her heat.
Two runners competed wearing hijab, 20-year-old Palestinian Woroud Sawalha and Sarah Attar from Saudi Arabia, reflecting the diversity of this Games -- the first to see women athletes included in every one of the 204 delegations.
Neither qualified for the next round, but Attar made history alongside teammate Wojdan Ali Seraj Abdulrahim Shaherkani, in judo, as the first two women to compete for Saudi Arabia. Brunei and Qatar also sent women competitors for the first time.
"It is a historic moment," Attar said, according to the official Games website. "I hope it will make a difference. It is a huge step forward."
These Games also mark the first time women's boxing is part of the Olympic program, with three semifinal bouts taking place Wednesday. Team GB's Nicola Adams made it through to the women's 51-kilogram flyweight gold medal bout after defeating India's Chungeijang Mery Kom Hmangte of India.
Adams will take on China's Ren Cancan for gold, after Ren beat Marlen Esparza of Team USA in their semifinal.
Both Esparza and Hmangte are awarded bronze, as there are no bronze-medal matches.
Meanwhile, Katrin Wagner-Augustin of Germany lost out on her second attempt at becoming the second woman in Olympic history to win a gold medal at four consecutive Games after helping take silver in the women's Kayak Four (K4). She still has one more shot at gold in the women's kayak single final on Thursday. Lisa Leslie, who won gold with the U.S. basketball teams in 1996-2008, is the only other woman to do so.
Gold in the women's K4 went to Hungary and bronze to Belarus.
On a good morning for Hungary on the water, it also took the gold in the men's double kayak final. Silver went to Portugal, giving the country its first medal of the Games.
Norway and Germany took gold in the men's single kayak and single canoe sprint events respectively.
Australia, whose athletes got off to a slow start in the medal stakes but are now gathering steam, took gold in the men's 49er sailing, while New Zealand claimed silver.
China is playing South Korea for the gold medal in the men's team table tennis final, after bronze went to Germany.
If successful, China will have won gold in every table tennis event played in London and in Beijing in 2008, according to the official Games website.
Over at Greenwich Park, the individual show jumping final put horses and riders through their paces.
Switzerland's Steve Guerdat came out with the gold after posting the only two clear rounds of the event.
Silver went to the Netherlands' Gerco Schroder, with Ireland's Cian O'Connor pushed into bronze position following a jump-off. That bronze is Ireland's first medal of the Games.
Great Britain, which took gold in the team show jumping event earlier this week and its first ever dressage team gold Tuesday, could only manage equal fifth for rider Nick Skelton, disappointing the home crowds.
Team GB, for which Queen Elizabeth II's granddaughter Zara Phillips helped win silver in the eventing,