The field of urban economics introduces space into economic models in order to study the location of economic (and social) activity. It is based on the definition of urban areas, which combines both a minimum density criterion and aminimumpopulation criterion. From the macro to the micro levels, it deals with urban growth/decline (the size and number of cities), urban structure (neighborhood specialization, transportation) and urban social/ecological problems (most notable, among others: segregation and sprawl). Those three levels are intertwined: for example, location patterns within an urban area -determining access to facilities, suppliers, workers, etc.- influence its ability to grow; slow metropolitan growth is more likely to widen the growth gap between city center and suburbs, hence exacerbate urban sprawl. Obviously, urban structure and dynamics crucially rely on how land is valued and developed into residential and commercial real estate: through the construction sector and the housing markets, which in turn depend on various technological constraints and regulations. And given how central mortgage finance is to the banking system, the functioning of the housing sector has tremendous consequences on the economy as a whole. Finally, despite many common mechanisms, urban fortunes are also deeply influenced by cultural and geographical idiosyncrasies. How information on urban systems and economies can be collected and treated, how urban economic theory and urban data can jointly be used to produce a relevant body of knowledge on cities, will be described in detail.