The Bryans were in California in late July for the Los Angeles Open. They played their first match at night, on the stadium court at U.C.L.A. They have similar form: fluid ground strokes, one-handed backhands, soft reflexes at the net. Bob, the lefty, has the most obvious weapons — a bigger serve and a huge forehand, which he hits with a slightly more open stance. At six-feet-four and 190 pounds, he is about an inch taller than his brother and 10 pounds heavier. Mike, who is right-handed, takes more balls on the rise, has one of the best returns of serve in doubles and is quicker on his feet and better able to take control of the net.

It’s not difficult to know what makes a good doubles player — an effective serve, quick hands on the volley, the ability to use the court vertically as well as sideline to sideline. These qualities are not so rare in pro tennis, and a good doubles team is still vulnerable to any random pairing of two first-tier singles players. (Or even one, with the right skill set: it used to be said that the best doubles team in the world was John McEnroe and whomever he put on the court next to him. In the women’s game, the same was true of Martina Navratilova.)

What’s remarkable about the Bryans’ play is the way it integrates not only their strengths but also their weaknesses, mostly through their unique relationship. Although they have been the most dominant doubles team of the past decade, the Bryans are not unbeatable. Despite being seeded first this year at Wimbledon, the twins lost in the finals to a bigger-serving team. Patrick McEnroe calls them the bedrock of the American Davis Cup team (which he has been captain of since 2001), yet adds, “They can be vulnerable when they’re overpowered by talent, by a team with two very good players — even singles players.” But teamwork and chemistry usually enable them to trump an opponent’s raw ability. Gullikson characterized the Bryans as “the best team in doubles, once the ball is in play.”

It begins with court coverage — the fruit of years of playing together and learning the game together — but there’s more to it than that. “Watch how little they talk to each other between points,” says Justin Gimelstob, a recently retired player who grew up competing against the Bryans and played doubles in 13 U.S. Opens with 13 partners. “That’s more the norm,” Gimelstob says of his failure to find a consistent teammate. “I played doubles with 113 different people in my career. We had to have a conference before every point.”

A lot of good doubles teams are, like the Bryans, built on a combination of one right-handed player and one left-hander. It can throw off an opponent’s rhythm and keeps both partners from having to look into the sun while serving. Most teams have the left-hander play the left side of the court and vice versa, allowing the players to cover the doubles alley — the part of the court that is out of bounds during singles matches — with forehands.

But the Bryans use the opposite formation. They have Bob return serve from the deuce (or right) side of the court, and Mike from the ad (or left) court. It leaves them on their natural backhand sides and can put both — particularly Bob — at a disadvantage on the return. “At the same time, it lets Bob poach a lot, coming across the middle of the court with his swinging forehand volley,” David Macpherson, their coach, says. “They win a lot of points that way, and they are constantly moving to set that up.”

The Bryans try to use this maneuver when Mike is serving into the ad court (on important, uneven-score points like 30-15 and 40-30) and when Mike — the more sure-handed returner — is returning serve. “So when Mike hits a low return and makes the other team pop a volley up high, Bob is there,” says Gene Mayer, a Top 5 A.T.P. player in the 1980s, who won a French Open playing with his brother, Sandy. The footwork and the shot-making are the stuff of standard doubles, but it helps that the Bryans have seen each other play the same balls countless times and can engineer the point, Mayer says.