The Frenchman has been a bit of an odd case this season, despite a remarkably consistent campaign last year.
Initially, he was tipped to start alongside Thomas Vermaelen in the center of defense, but an injury right before the start of the season meant that Per Mertesacker was given his chance.
The German has now played in 31 of Arsenal's 15 Premier League games, demonstrating a consistency that few other Gunners players have matched this season, while adding height and defensive commitment that no one else can provide.
And it was apparent from the first game of the season that that was the case. So the battle, then, was between Koscielny and Vermaelen. And for a while, there was one clear winner.
However, the victor did not deserve the spoils. While not a Sebastien Squillaci-esque calamity at the back, Vermaelen's performances were shaky, and did not inspire the sort of confidence that one expects from a consistent starter and the club captain.
Even though nobody can demonstrate proof, it is not unreasonable to suspect that the only reason Vermaelen kept his place in the side for so long was due to the piece of cloth he wears around his left arm.
It is reasonable to assume that a player of lesser stature would have been dropped very quickly after making some of the boneheaded errors that Vermaelen did at the back. But the captain remained the left centre-back for months.
Eventually, though, Arsene Wenger had had enough. Before Arsenal's match against Bayern Munich in the second leg of the Champions League Round of 16, the manager unexpectedly benched Vermaelen for Koscielny.
He has played every minute of Arsenal's games since.
Let's think about why.
First of all, there is a reason why Koscielny has replaced Vermaelen, and not Mertesacker. While neither the Frenchman nor the Belgian are particularly tall or physical as center-backs go, Mertesacker is both.
He is also the most willing to stay back and provide insurance while the rest of the team pushes forward to attack. Mertesacker is a marked departure from Arsenal's other defenders, who rely on pace and aggressiveness to snuff out attacks. Rather, he is measured and composed in his defending, and compensates for his lack of pace by reading the game superbly.
So Arsene Wenger's choice was therefore between Koscielny and Vermaelen.
One of the latter's major flaws is his eagerness to race forward. While this occasionally produces a spectacular goal or troubles the opposition's defense, it puts an immense amount of pressure on Arsenal's midfield and the few players who remain behind to defend the inevitable counterattack.
Koscielny does not do this. As the above highlight tape from the Manchester United game shows, he picks and chooses his moments to charge forward, while aggressively pursuing the ball and reading the game well.
In one instance, he is subtle in his defending, like Mertesacker, in simply stepping in front of an opposing forward to intercept the ball. In another, he charges forward like an enraged bull and wins the ball back by brute force.
That versatility and dynamic defending ability is what makes him such a valuable asset.
Vermaelen is decent in the air, but so is Koscielny; both are quite capable of rising to meet a cross in flight.
And both are more technical defenders, using their feet to get out of tricky situations and distributing the ball from the back. Vermaelen is probably a bit better in this area, but Koscielny's pass completion rate is only three percent less, according to Squawka.com.
Essentially, Arsene Wenger's selection dilemma boils down to two options, who are quite similar in their styles of play and complement Per Mertesacker fairly well.
On the whole, though, Laurent Koscielny is simply a better and more consistent version of Thomas Vermaelen, with only one or two minor exceptions.
Assuming he is not blunted by any more injuries, expect Koscielny to keep Vermaelen out of the side for quite a while. As of now, the Frenchman has not given Arsene Wenger any reason to drop him.