Here's everything you need to know about the 2017 Nitto ATP Finals.
The ATP Finals begins in London on Sunday, with the top eight healthy men in the world set to compete for the prestigious year-end title.
The top two seeds at this year's championship are as familiar as it gets. Rafa Nadal enters the tournament as the top-seed and will end the year as the No. 1 player in the world no matter his results in London. Nadal, who won two majors this season, is making his 13th consecutive appearance at the Finals, and while he has reached the final twice—in 2010 and 2013—he is yet to win the title.
The second seed is Federer, who recently opted to pull out of the Paris Masters, a move that guaranteed Nadal the number one spot to end the year. Federer, 36, also won two majors this season to go along with seven titles overall, and he's a remarkable 49-4 on the year. The Swiss maestro has won the year-end championship a record six times.
Apart from Fedal at the top, this year's field is largely a new crop of players, as many of the usual suspects will miss the tournament due to injury. The most glaring absence is that of Novak Djokovic, who has not played since retiring against Tomas Berdych in the quarterfinals of Wimbledon. Also missing is Andy Murray, who also hasn't played since Wimbledon but returned to the court for an exhibition against Federer in Scotland, and Stan Wawrinka, who also shut down his season after Wimbledon.
An American is in the field for the first time since Mardy Fish qualified in 2011. Jack Sock snuck into the eighth and final spot by taking advantage of an injury-depleted field to win the ATP World Tour Masters 1000 in Paris, which vaulted him from No. 24 all the way to No. 9 in the rankings. He qualifies because No. 7 is Wawrinka, who will not play.
The eight players are split into two four-player groups: Group Pete Sampras and Group Boris Becker. Each player will play all the other players in his group in the round robin portion of the event. After the completion of the round robin, the top two finishers in each group will advance to the semifinals. The top player from Group Pete Sampras will play the second-place finisher from Group Boris Becker, and the first-place finisher from Group Pete Sampras will play the runner-up from Group Boris Becker. The winners of those semifinal matches will meet to determine the 2017 ATP Nitto Finals champion.
Here are the breakdowns of the two groups.
Group Pete Sampras
 Rafael Nadal (ESP)
 Dominic Thiem (AUT)
 Grigor Dimitrov (BUL)
 David Goffin (BEL)
Group Boris Becker
 Roger Federer (SUI)
 Alexander Zverev (GER)
 Marin Cilic (CRO)
 Jack Sock (USA)
Sunday, Nov. 12
 Federer vs.  Sock, 9 a.m. ET
 Zverev vs.  Cilic, 3 p.m. ET
Monday, Nov. 13
 Thiem vs.  Dimitrov, 9 a.m. ET
 Nadal vs.  Goffin, 3 p.m. ET
Additional matches have yet to be announced.
All matches will be broadcast live on the Tennis Channel. Qualifying subscribers can stream the tournament online on Tennis Channel Everywhere.