When conflict rears its ugly head around the world, there is usually a call for the United States to “do something.” One option that is frequently mentioned is the no-fly zone. The United States and its allies enjoy a significant advantage over most potential adversaries in the air. No-fly zones, therefore, are attractive due to the perceived lower cost and risk when compared to other options. Despite this, setting up a no-fly zone is anything but a “no brainer.” Depending on the circumstances, there may be steep costs and unseen risks. This short primer is intended to introduce readers to the way no-fly zones really work.