Around the world, companies are developing small, quiet electric-powered vertical takeoff and landing (eVTOL) aircraft to take mobility services from the roads to the skies. Urban air mobility (UAM) is for real. Our analysis finds that it will be a premium mobility option - mainly for those who will pay a little more to save time traveling to the airport, getting to important meetings or beating the traffic to a weekend home. We've identified a set of global megacities where the conditions to support a UAM market will soon be in place, based on current rates of urbanization, economic growth and projected increases in traffic congestion. By 2050, UAM could spread to regional service with over 400 million annual passenger enplanements, comprising four percent of all domestic air traffic globally. To win in UAM, aircraft manufacturers, developers of navigation and propulsion technologies, and other players will need to choose their markets and partners carefully.