City System is an accessory for the Advanced Dungeons & Dragons fantasy role-playing game. It was written by Jeff Grubb and Ed Greenwood, and published in 1988 by TSR. It includes extensive and detailed maps of the city of Waterdeep, and was intended to serve as a companion to Waterdeep and the North. The sheer expanse of the maps drew praise from Ken Rolston of Dragon magazine, although he criticized their lack of personality and utility.