Big story: Anchored by reigning world champion Kim Woo-Jin, South Korea is expected to dominate both the individual and team events. The South Korean squad is so strong 2012 Olympic gold medalist Oh Jin-Hyek was left off the roster.
Top U.S. prospects: Brady Ellison, who led the U.S. team to a surprise silver medal at the London Games, is ranked second on the World Cup circuit as he heads to his third Olympics. Along with teammates Zach Garrett and Jake Kaminski, Ellison earned bronze last June in a World Cup team competition.
Big story: Led by reigning Olympic gold medalist Ki Bo-Bae, the South Korean women will attempt to break the world record in the team event. They set the record with 2,045 points on the World Cup circuit this summer.
Top U.S. prospects: Mackenzie Brown will be the sole female archer for the United States after the American women failed to qualify in the team event. The 21-year-old Texan, ranked fourth in the world, took bronze in the Olympic test event in Rio last year.
Big story: A rule change that limits countries to two competitors per event could weaken China's dominance.
Top U.S. prospects: The Americans, who have never medaled in this sport, qualified seven players for Rio — their largest contingent ever.
Big story: Can Team USA win its third straight gold medal?
Top U.S. prospects: The notion of another U.S. Dream Team faded when LeBron James, Chris Paul, Stephen Curry, Blake Griffin and others decided to skip the trip to Rio, but this team is still deep enough to dominate. Coach Mike Krzyzewski focused on defensive play, but he has enough scoring depth to win gold in his final Olympic coaching appearance.
Big story: The U.S. women are trying for a sixth straight gold medal and eighth gold overall since women's basketball was added to the Olympic program in 1976.
Top U.S. prospects: Forward Breanna Stewart, one of five University of Connecticut players on a squad led by UConn coach Geno Auriemma, is one of three first-time Olympians on the 12-woman roster. Stewart was selected over two-time Olympian Candace Parker, a controversial decision.
- Beach volleyball
Big story: After getting silver in 2012, will Brazil's Alison Cerutti claim his first gold on home soil with partner Bruno Schmidt, or can Brazil's other top team, Pedro Solberg and Evandro Goncalves, spoil the party?
Top U.S. prospects: Phil Dalhausser won a gold medal with Todd Rogers in 2008. He and Nick Lucena are third in the FIVB Olympic rankings headed into Rio. Jake Gibb and Casey Patterson were sixth.
Big story: Misty May-Treanor, who won the last three gold medals with Kerri Walsh, is retired, meaning a new team will take home the gold for the first time since 2000.
Top U.S. prospects: Walsh is still playing, this time with April Ross, and the duo was rated No. 3 in the FIVB Olympic rankings before Rio. The other American team, Lauren Fendrick and Brooke Sweat, is a long shot.
Big story: The U.S., trying to rebound from a disastrous 2012 Games in which it didn't medal for the first time in Olympic history, comes to Rio with a young team of six boxers between 18 and 20.
Top U.S. prospects: Shakur Stevenson, a junior and youth world champion, is undefeated internationally at 23-0 and was the first American male to win Youth Olympic Games gold. Antonio Vargas is the 2015 Pan American Games champion, having beaten Olympians from Puerto Rico and Cuba to en route to his title.
Big story: Claressa Shields can become the first U.S. boxer, male or female, to win back-to-back Olympic gold medals. She has lost just once in her career and is unbeaten since the London Games.
Top U.S. prospects: Mikaela Mayer, who narrowly missed a spot on the Olympic team four years ago, fought her way through a challenging draw to win gold at the Americas qualifier and earn a trip to Brazil.
- Canoe slalom
Big story: The U.S. will be looking to break a 12-year medal drought.
Top U.S. prospects: Michal Smolen was the men's kayak bronze medalist in the 2015 world championships. Casey Eichfeld, a three-time Olympian, was a double gold medalist in canoe (single and double) in the 2015 Pan American Games.
Big story: The conditions in the lagoon could overshadow the competition. During a 2015 test meet, competitors complained of polluted water that made them sick and plants that got entangled in their paddles.
Top U.S. prospects: Maggie Hogan, a 14-time national champion, is the lone U.S. qualifier for the Rio Games in canoe sprint, earning her first Olympic berth by placing second in the women's kayak 500-meter event at the 2016 Pan American championships.
Big story: Latvia's Maris Strombergs has won the only two gold medals ever on the men's side and is looking for for a third, while on the women's side Colombia's Mariana Pajon is trying to defend her 2012 gold.
Top U.S. prospects: Alise Post, ranked third in the world, and Nic Long, ranked second on the men's side, are medal contenders.
Big story: One of the top road racers in the world, the Czech Republic's Peter Sagan, will compete in the mountain bike event.
Top U.S. prospects: Don't expect much from the U.S. team. Its top-ranked female rider, Lea Davison, was ranked 15th while the lone American male rider, Howard Grotts, was 47th.
Big story: Top American cyclist Tejay van Garderen pulled out of Rio, citing concerns over the Zika virus. Based on disappointing 2015 world results, the U.S. men were given only two slots of a potential five.
Top U.S. prospects: Kristin Armstrong, who turns 43 on Aug. 11, is going for her third straight time-trial gold medal. Taylor Phinney and Brent Bookwalter are the only two U.S. men competing.
Big story: As recently as February, Bobby Lea was considered a long shot to make the team because of a 16-month ban stemming from a positive drug test. But the ban was reduced to six months by a court of arbitration, allowing the two-time Olympian to return.
Top U.S. prospects: Matt Baranoski is ranked 16th in the world in the keirin sprint event. Lea finished 12th in the omnium competition at the 2012 Games.
Big story: The U.S. women's team pursuit won its first world title in March, besting Canada in the gold-medal round to win a world championship. The five American cyclists in Rio range in age from 32 (Sarah Hammer) to 19 (Chloe Dygert).
Top U.S. prospects: Dygert is emerging as one of the best young cyclists in the world. Hammer is the elder stateswoman, a two-time Olympian who left London with two silver medals.
Big story: David Boudia (U.S.), Qiu Bo (China) and Tom Daley (Britain) battle in the 10-meter platform.
Top U.S. prospects: Boudia took gold in the 10-meter platform at the London Olympics but hasn't won an international competition since. He'll also team with Steele Johnson in the synchronized 10-meter competition.
Big story: Chinese women won five medals — four gold — at the London Olympics, and their dominance looks as if it will continue.
Top U.S. prospects: Abby Johnston won silver in the synchronized 3-meter springboard in London but will compete in the solo event this time. Kassidy Cook will join her in the springboard event after just missing out on qualifying for London.
Big story: Double gold medalist Michael Jung was forced to switch horses shortly before the animals were to be transported to Brazil when his top horse, Takinou, came down with an infection. The German rider won gold in London in individual eventing and another as part of the team effort.
Top U.S. prospects: The Americans are the favorites to take the gold in the team jumping competition.
Big story: Ibtihaj Muhammad will be the first U.S. athlete to compete at the Olympic Games in a hijab.
Top U.S. prospects: Mariel Zagunis is the most decorated fencer in U.S. history with three medals, including two golds, in women's saber. Daryl Homer has a shot at becoming the first U.S. man to win gold in saber.
- Field hockey
Big story: Can the German men win a third straight gold medal?
Top U.S. prospects: The U.S. women are ranked fifth in the world. The U.S. doesn't have a men's team entered.
Big story: The absence of top players Jason Day, Dustin Johnson, Jordan Spieth and Rory McIlroy is making people question golf's Olympic return after a 112-year absence.
Top U.S. prospects: Any of the four Americans — Bubba Watson, Rickie Fowler, Patrick Reed and Matt Kuchar — could win.
Big story: Zika didn't scare off the top women. They're either more patriotic or more eager for potential marketing and endorsement opportunities.
Top U.S. prospect: At 21, Lexi Thompson is already an LPGA veteran, having won an event at 16.
Big story: How will the U.S. men bounce back after a disappointing showing four years ago, having finished fifth in the team final?
Top U.S. prospects: They were admittedly nervous in 2012 and have matured since that rocky first moment in prime time. Three of the five — Sam Mikulak, Danell Leyva and Jake Dalton — are back.
Big story: The drive for five. Simone Biles could realistically win four gold medals, possibly five, and land on magazine covers and cereal boxes worldwide.
Top U.S. prospects: The U.S. is heavily favored to defend its team title — with Laurie Hernandez, Gabby Douglas, Aly Raisman and Madison Kocian joining Biles. Biles has won the last three all-around world championships. Golds on the floor, balance beam and vault are not a stretch for a gymnast with her ability and big-event poise.
Big story: Who will take the place of the now-retired Evgenia Kanaeva, widely considered to be the leading ribbon dancer of her generation? It is expected to be an all-Russian battle for podium supremacy between close friends Yana Kudryavtseva and Margarita Mamun.
Top U.S. prospects: U.S. champion Laura Zeng, 16, could become the first American to finish in the top 10.
Big story: Can Dong Dong win gold gold? Dong Dong of China, the high-flying artist who wowed fans in London, is the defending men's champion.
Top U.S. prospects: Logan Dooley, 28, will be the oldest first-time U.S. Olympic gymnast since 1972. Nicole Ahsinger, 18, is the U.S. women's competitor.
- Team handball
Big story: The men's draw has previous Olympic champions France and Croatia in the same group.
Top U.S. prospects: Neither the men's team nor the women's squad qualified for Rio.
Big story: French heavyweight Teddy Riner, a two-time Olympic medalist hailed as the most successful judoka of all time, hasn't lost in nearly six years. But the eight-time world champion, who stands an imposing 6-foot-8, has been slowed by shoulder injuries.
Top U.S. prospects: Travis Stevens, a three-time Olympian, is still looking for his first medal, having lost early bouts to the eventual champion in the last two Summer Games. Nick Delpopolo, a former Pan American champion, is competing in his second Olympics.
Big story: Kayla Harrison, who became the first U.S. athlete to win a judo gold medal in London, will try to become the first non-Asian woman to win multiple titles.
Top U.S. prospects: Harrison is the defending Olympic champion at 172 pounds and is ranked No. 1 in the world. Marti Malloy, the current Pan American champion and a bronze medalist in London, comes to Rio ranked third in the world in at 126 pounds.
- Modern pentathlon
Big story: The five-event competition features riding, swimming, fencing, pistol shooting and a cross-country run. Reigning world champion Pavlo Tymoshchenko of Ukraine typically excels at riding, but he'll need to overcome previously lackluster performances in swimming and fencing if he wants to win gold.
Top U.S. prospects: The United States will be represented by Army Sgt. Nathan Schrimsher, who is ranked 40th in the world.
Big story: Brazilian Yane Marques became the pentathlon's first Olympic medalist from the Southern Hemisphere, taking bronze in London. She's hoping her familiarity with the arenas helps secure gold for the home country.
Top U.S. prospects: After missing the London podium by two seconds, Margaux Isaksen hopes to win a medal at her third Games. She'll be joined in Rio by her younger sister, Isabella, who is making her Olympic debut.
Big story: Water quality will be the top story with organizers having removed thousands of dead fish from Lagoa Rodrigo de Freitas in preparation for the Games. The fish are said to have died from a lack of oxygen caused by pollution. The International Rowing Federation declared the water "very acceptable" at the junior world championships last year, though its medical commission warned athletes to "avoid inadvertent immersion, including splashing."
Top U.S. prospects: Henrik Rummel and Charlie Cole, who won bronze in the men's four in London, are looking to return to the medal stand along with new teammates Matt Miller and Seth Weil. The men's eight is not expected to medal.
Big story: The U.S. women's eight enjoys one of the strongest dynasties in international sports, having won every world championships and Olympic competition since 2006. To maintain their crown, they'll have to hold off competitive crews from New Zealand and Britain.
Top U.S. prospects: Tracy Eisser and Megan Kalmoe, who won gold at the 2015 world championships in the women's quadruple sculls, could find themselves atop the podium in Rio along with crewmates Adrienne Martelli and Grace Latz.
Big story: Rugby returns to the Olympics after more than 90 years. This time they'll play a "sevens" version of the game that has about half the number of players on the field and twice the wide-open action.
Top U.S. prospects: Captain Madison Hughes and the sixth-seeded Americans must fight their way out of a four-team pool bracket that includes top-seeded Fiji.
Big story: New Zealand no longer dominates, with Australia, Canada and Britain rising up in the ranks.
Top U.S. prospects: Like the American men, the women are ranked in the middle of the field and will have the top seed, Australia, in their preliminary pool.
Big story: Competitors will race in picturesque Guanabara Bay, which has drawn concern over heavy pollution that includes raw sewage, so-called super bacteria and floating debris.
Top U.S. prospects: Annie Haeger and Briana Provancha won the women's 470 class at last year's Rio de Janeiro test event.
Big story: American Matt Emmons returns for his fourth Olympics with a roller-coaster history that includes three medals and a few painful misses.
Top U.S. prospects: Vincent Hancock is a two-time Olympic defending champion in skeet. Josh Richmond ranks among the top double trap shooters in the world.
Big story: Kim Rhode, 37, is only the second U.S. woman to qualify for six Olympics. So far in her historic career, she has medaled in every Games.
Top U.S. prospects: Corey Cogdell-Unrein, a bronze medalist in the 2008 Beijing Games and wife of Bears defensive lineman Mitch Unrein, could be getting hot at just the right time.
Big story: Brazil has never won an Olympic soccer title, and after the national team failed to reach the final of the 2014 World Cup it hosted, the pressure to win a gold medal here is immense.
Top U.S. prospects: The U.S. did not qualify.
Big story: The reigning World Cup champion U.S. team will be going for its fourth straight Olympic title.
Top U.S. prospects: Winning again this summer would make the U.S. the first team in history to hold World Cup and Olympic titles at the same time.
Big story: Michael Phelps, the most decorated Olympian of all time, caps his medal-studded career with a final push for gold after a brief retirement following the London Olympics. This is the fifth Olympics for Phelps. The 22-time medalist will swim three individual events (100-meter butterfly, 200-meter butterfly, 200 IM), including his final showdown with longtime rival and 11-time Olympic medalist Ryan Lochte in the 200 IM.
Top U.S. prospects: Josh Prenot recorded the world's best time this year in the 200 breaststroke. Ryan Murphy will challenge for gold in the 100 backstroke. Same with Nathan Adrian in the 100 freestyle, where he's the defending champion, and the 50 freestyle.
Big story: Can Katie Ledecky make history? The 19-year-old is the youngest member of the U.S. team and might be the most dominant active swimmer of either gender. She is the big favorite in the 400-meter freestyle (she holds the world record) and 800 freestyle (she owns the 10 fastest times in history). She also could win gold in the 200 freestyle in addition to the 800 freestyle relay.
Top U.S. prospects: After giving birth to a son last year, Dana Vollmer is back to defend her 100 butterfly title from the London Olympics. First-time Olympian Maya DiRado qualified in three individual events. Lilly King, another newcomer, clocked the world's fastest time this year in the 100 breaststroke.
- Synchronized swimming
Big story: Russia has dominated the sport, winning every team and duet gold medal since the Sydney Olympics in 2000.
Top U.S. prospects: The lone U.S. competitors, first-time Olympian Anita Alvarez and Mariya Koroleva, make up the duet team. Koroleva placed 11th in this event at the London Olympics with her previous partner.
- Table tennis
Big story: Lily Zhang, who won bronze at the 2014 Youth Olympic Games, returns for her second Olympics.
Top U.S. prospects: Another of the three sports in which no American athlete has ever medaled. Zhang is the highest-ranked U.S. player at No. 94 in the world.
Big story: With a podium finish, American Steven Lopez — who won gold in 2000 and 2004 and bronze in 2008 — will become the sport's most decorated Olympian. The 37-year-old Texan is the 10th-ranked welterweight in the world and won the Pan American Olympic qualifying tournament.
Top U.S. prospects: Stephen Lambdin, who will make his Olympic debut in the heavyweight division, is ranked 10th in the world.
Big story: There have been some changes to the sport since the London Games, and organizers are hoping they make the event more exciting. For example, the ring is smaller to make it more difficult to flee an opponent's rapid-fire kicks. And, in an effort to encourage more spinning moves, an extra point will be given to kicks in which the competitors' backs are turned.
Top U.S. prospects: Paige McPherson, who won bronze in London, will compete in her second Olympics after finishing third in the welterweight division at the world championships last year. Teammate Jackie Galloway, who competed for Mexico in the past, also is a medal contender.
Big story: Spain's Rafael Nadal will return to compete after suffering a wrist injury in May. With the Spaniard back, the question is can Britain's Andy Murray repeat as singles champion?
Top U.S. prospects: John Isner and Sam Querrey would have represented America's best hope, but both are taking a pass on Rio. That leaves Steve Johnson and long shots Jack Sock, Denis Kudla and Brian Baker.
Big story: Serena Williams looks to add to her legacy by winning more gold medals. She already has three in doubles with sister Venus and triumphed in 2012 at Wimbledon in singles.
Top U.S. prospects: The Williams sisters will be playing in their fifth Olympics, a record for tennis.
- Track and field
Big story: Dynamic Jamaican sprinter Usain Bolt is a beacon of light in a sport that has been tainted by drug use and will be without Russian athletes, banned because of state-sponsored doping. Bolt, the world record holder in the 100 meters (9.58 seconds) and 200 (19.19), will try for a triple-triple: gold in both sprints and the 400-meter relay in three straight Olympics. He has recovered from a strained hamstring that hampered him earlier this year.
Top U.S. prospects: Justin Gatlin, gold medalist in the 100 in 2004 and bronze medalist in 2012, will challenge in both sprints. LaShawn Merritt will try to become the first man to win the 200-400 double since Michael Johnson in 1996. Merritt has run the fastest times in the world this year in the 200 (19.74) and 400 (43.97). Ashton Eaton is favored to repeat in decathlon.
Big story: Russian women won medals in 15 track and field events in 2012. With the team banned because of the country's state-sponsored doping, the door is open for new medal winners.
Top U.S. prospects: Allyson Felix won't defend her Olympic title in the 200-meter race but is favored in the 400, where she has run the world's second-fastest time this year (49.68 seconds). She could win medals in both relays too. Tianna Bartoletta made the team in the 100 and the long jump, the event in which she won two world titles. Tori Bowie likely will contend in the 100 and the 200. Sandi Morris set a U.S. women's outdoor pole vault record of 16 feet, 2 inches in late July and will push her teammate, Olympic and world champion Jenn Suhr.
Big story: A healthy Alistair Brownlee of Britain, the defending Olympic champion, would be the logical favorite. But Brownlee has been injury-riddled since winning in London four years ago. His younger brother, Jonathan, has been more consistent with three second-place finishes on the circuit this year.
Top U.S. prospects: Greg Billington, Ben Kanute and Joe Maloy are not expected to be in the medal hunt.
Big story: Will the dominance of American Gwen Jorgensen finally pay off with an Olympic medal? Jorgensen suffered a flat tire in London, finishing 38th.
Top U.S. prospects: Jorgensen is the gold-medal favorite. Katie Zaferes, coming off her first World Triathlon Series gold, will be in the hunt for a medal as well.
Big story: The U.S., ranked fifth, will have an uphill battle to rebound from missing out on a medal in 2012 with a group coach John Speraw said does not have the experience of previous teams.
Top U.S. prospects: The U.S. is hoping for a strong effort from outside hitter Taylor Sander, who was the MVP and Best Spiker of the FIVB World League Final Round in 2014.
Big story: Brazil will be vying for its third consecutive gold medal while the U.S. is looking for revenge against the Brazilians after taking silver the last two Olympics.
Top U.S. prospects: The U.S. is No. 1 in the world behind talent like setter Alisha Glass, who was indoor player of the year in 2013 and 2014, and outside hitter Jordan Larson, the 2015 player of the year.
- Water polo
Big story: Serbia, which has won the last four World League titles, is the favorite. The U.S. men figure to challenge.
Top U.S. prospects: U.S. captain Tony Azevedo is the first five-time Olympian in USA Water Polo history.
Big story: The dominance of the U.S. women, who are ranked No. 1 in the world, won Olympic gold in 2008 and 2012 and are the reigning World Cup and world champs.
Top U.S. prospects: Sisters Aria, 17, and Makenzie Fischer, 19, are among the newcomers to a team that has brought back four women from 2012.
Big story: The weightlifting competition will be weakened by the absence of athletes from Russia, Kazakhstan, Belarus, Ukraine, North Korea and Azerbaijan, who have been disqualified for doping. The Bulgarian team was also suspended.
Top U.S. prospects: Kendrick Farris, a three-time Olympian, is the only U.S. male competitor.
Big story: The only two U.S. medals in women's weightlifting came in 2000. Heavyweight Jenny Arthur, a three-time national champion, may have the best chance at ending that slump after winning a Pan American championships silver medal.
Top U.S. prospects: Sarah Robles, who is coming off a two-year suspension after a positive steroid test, is a two-time Olympian. She placed seventh in London.
Big story: Cuba's Mijain Lopez, a five-time world and two-time Olympic champion, has a chance to become only the fifth male wrestler to win three gold medals.
Top U.S. prospects: Two-time world bronze medalist Andy Bisek is the American squad's best shot for a Greco-Roman medal.
Big story: Defending Olympic champion Jordan Burroughs will seek back-to-back gold in the 163-pound class. With just two losses in his international career, the three-time world champion is the closest thing the U.S. team has to a lock on the medal stand.
Top U.S. prospects: Two-time NCAA champion J'den Cox stunned many by winning the U.S. Olympic trials in the 189.5-pound class.
Big story: Japanese wrestlers Saori Yoshida and Kaori Icho are looking to become the first wrestlers, male or female, to take gold in four consecutive Games. If they can pull it off, they also will become the first women to win the same Olympic event four times.
Top U.S. prospects: The U.S. women's team will be led by three-time world champion Adeline Gray, who won the test event in Rio earlier this year. Teammate Helen Maroulis also has a solid shot at the podium.
Compiled by Tribune Olympic Bureau reporters Tim Bannon, Kevin Baxter, Lisa Dillman, Helene Elliott, Nathan Fenno, Teddy Greenstein, Chris Hine, Stacy St.Clair and David Wharton