Arenal defender Koscielny happy playing with Mertesacker
The France international claims their success is down to communication.
"We play well together as a pair," Koscielny told arsenal.com. "We communicate on the pitch and we communicate well.
"His experience is vital and that helps us work together. We try and talk to each other a lot and it is important at the back to have an understanding.
"Per is a very good player. He reads the game well and he is clever. He attacks the ball and wins headers whereas I go behind, can be quick and cope with the long balls. He is good technically so he is good for the defence. Per is calm on the pitch and he uses his experience. This helps me and helps the team."