Cities define our future, and Big Data is a part of that. Today, more than half of all humanity lives in urban areas; by 2050, three-quarters will. Amidst this powerfully transforming landscape, information has emerged unchallenged as the pervasive currency. It has the potential to change how cities monitor, manage, and enhance the livability of their communities—affecting transport, education, public safety, and city administration. What is Big Data and how does it drive smarter cities? How can Big Data optimize the use of urban infrastructure? Can computer models identify crime hotspots and traffic bottlenecks? The 2014 Emerging Leaders report begins to tackle some of these questions and more by looking at the experience of the City of Chicago.