Half a century ago, major cities in the United States had little, if any, large and charismatic wildlife. In the years since, however, researchers and residents have documented a remarkable transformation: wild animals, including many species once believed to require remote wilderness areas, have settled in cities in North America, Europe, East Asia, and elsewhere. Most urban regions on these continents now house diverse and abundant wildlife, with repercussions for everything from science and technology to ethics, health, conservation, sustainability, and planning. How did this sea change occur? And what does it tell us about wildlife, people, and the cities we increasingly share on this urbanizing planet?