With the rapid progress of urbanization and civilization on earth, urban computing is emerging as a concept where every sensor, device, person, vehicle, building, and street in the urban areas can be used as a component to probe city dynamics to further enable city-wide computing for serving people and their cities. Urban computing aims to enhance both human life and urban environment smartly through a recurrent process of sensing, mining, understanding, and improving. Urban computing also aims to deeply understand the nature and sciences behind the phenomenon occurring in urban spaces, using a variety of heterogeneous data sources, such as traffic flows, human mobility, geographic and map data, environment, energy consumption, populations, and economics, etc. Recently, real-world data reflecting city dynamics becomes widely available, including, e.g., users’ mobile phone signal, GPS traces of vehicles and people, ticketing data in public transportation systems, user-generated content (like tweets, micro-blog, check-ins, photos), data from transportation sensor networks (camera and loop sensors) and environment sensor networks (temperature and air quality), as well as data from the Internet of Things. As a result, we are ready to carry out real urban computing activities that lead to better and smarter cities. By better sensing and understanding the city dynamics we are more likely to design effective strategies and intelligent systems for improving urban lives.