Of all types of outdoor concrete flatwork, tennis courts may be the most demanding surfaces. A few basic but perhaps uncommon construction procedures are necessary for the building and maintenance of high quality tennis courts that will last for decades even in northern climates. A bank of four public tennis courts at Thornwood Park in Wilmette, Illinois has achieved a remarkable 22-year service record. These successful courts have no joints within the playing area and are constructed of high quality air-entrained concrete with substantial reinforcement of the 5-inch-thick slabs. Reinforcement does not stop concrete from cracking, but it does keep the crack from opening. The more reinforcement used, the finer the cracks will be. There are hairline cracks in the Wilmette courts, but they are not wide enough to disturb the bounce of the ball or to interfere with the footwork of the players.