The two-time defending Olympic champion Brazil women are chasing a golden three-peat on home soil this summer. The top-ranked Americans are seeking redemption in Rio and their first gold ever.
This is the rivalry to watch in the women's volleyball tournament.
The Americans expected to win gold four years ago in London and instead were stunned by the Brazilians, who captured their second straight Olympic title.
Now, the Brazilian women have home court, so beating them in Rio would be even more monumental.
And coach Karch Kiraly's close-knit U.S. squad believes it has built the right mix to challenge for the top spot on the podium this August in Rio de Janeiro. The Americans have developed a culture they are counting on being the right one.
''I've never seen anybody win a competition like the Olympics without getting through massive adversity along the way, and the way you do that is to have the team that fights really hard for each other and makes each other better and adds up to more than the sum of their parts,'' Kiraly said. ''When our adversity came at us, it wasn't until the final match of the Olympics and we weren't powerful enough. We didn't add up to enough more than the sum of our parts to be able to withstand the storm that came at us.''
The American women have dealt with challenges already preparing for Rio. They had to get there the hard way - through a second-chance qualifier in January at Lincoln, Nebraska, after losing twice at last year's World Cup in Japan.
Brazil coach Jose Roberto Guimaraes led the men's team to gold at the 1992 Barcelona Games and then the women the past two Olympics, and he has several players from both of those winning teams back for the run right at home in Rio.
The Brazilian women would become the first to capture three straight gold medals in women's volleyball since Cuba in 1992, `96 and 2000. China won in 2004 at Athens.
Kiraly's team will be in the same six-team pool with China just as it was in London. The Americans beat China in the 2014 world championship, while China won last year's World Cup in Japan.
Here are some things to watch in the Rio Games' volleyball tournament, which became part of the Olympic program in 1964:
NO LONDON SWEEP: The Brazilian men were so close to making it a sweep of the top podium spot in London, then Dimitriy Muserskiy and Russia changed the plan. The Russians captured their first men's volleyball gold in 32 years with a comeback five-set victory.
Former Brazil captain Gilberto Godoy Filho, known as Giba, was one of the game's most celebrated stars who led Brazil to gold in Athens. He said farewell in London after 16 years with the national team.
FORMAT: In both the men's and women's tournaments, there will be two six-nation pools with the top four from each advancing.
The pools were divided based on teams with the highest world ranking as of Jan. 1 being placed first into Pool B after host Brazil was automatically put into Pool A.
On the women's side, Serbia returns to the Olympics for the first time since 2008 in Beijing.
YOUTH MOVEMENT: U.S. men's coach John Speraw has embraced a youth movement with the Americans, choosing eight first-time Olympians to his roster to join veterans such as four-time Olympian Reid Priddy and David Lee headed to his third Olympics.
This group won the 2014 World League title and last year's World Cup, so those championships alone have helped the U.S. gain valuable experience on the world stage.
''For us to have been at the top of the podium a couple times this quad, it does give a young team confidence they can win a tournament,'' Speraw said. ''Certainly that's our goal. They believe they can do that. They believe they can win a gold in Rio.''
RUSSIAN SCANDAL: The meldonium doping scandal extended to Russian volleyball. Outside hitter Alexander Markin tested positive for the substance in January. Markin was temporarily suspended while the FIVB, volleyball's international governing body, considered the case. The FIVB found that Markin ''committed an anti-doping rule violation but bore no fault or negligence in this case'' and reinstated him. The panel also found that the amount of meldonium in Markin's sample was so small that it likely did not enhance his performance.
DON'T COUNT OUT CHINA: While much of the focus in Rio will be on the battle between the U.S. and host favorite Brazil, the Chinese women's national team could surprise everyone. China is ranked No. 2 under coach Jenny Lang Ping - the former U.S. coach who led the Americans to silver in Beijing. Lang Ping was known as the ''Iron Hammer'' during her playing days, and helped guide the Chinese women to victory in the 1984 Los Angeles Olympics. She stepped down as coach of the Americans shortly after the Beijing Games to devote more time to her family, but took China's top post in 2013. Earlier this year, Lang Ping married Wang Yucheng, a religious studies professor.
RUSSIAN WOMEN REGROUP: The Russian women have had to heal during this four-year cycle, and now they will chase their first Olympic medal since earning silver at the 2004 Athens Games.
After failing to medal at the London Olympics after coming into the tournament as a contender, the Russian women suffered an unimaginable loss.
Their coach, Sergei Ovchinnikov, died at age 43 while working at a training camp in Croatia only a couple of weeks later. Russia lost in the quarterfinals in London to Brazil.
AP Sports Writer Anne M. Peterson contributed to this report.