Most Americans today live in a metropolitan area. This population density has advantages, including social connectivity and availability of public transportation. It also has downsides, such as the generation of a huge amount of heat over the metropolitan area. This urban heat island can cause a host of problems, including smog formation and the excessive reliance on air-conditioning in summer months. In this "How It Works" article, associate editor Rob Yagid offers some insights on how urban heat islands form and how homeowners can take steps to help reduce their impact.