The term ‘Urban science’ is increasingly used to describe a new generation of approaches to understanding cities and urban areas. There are now journals of Urban Science – and Computational Urban Science – and both undergraduate and postgraduate university degrees in Urban Science linked to Planning, Computer Science and Urban Analytics. But what, exactly, is urban science? How does urban science differ from other kinds of science, or other kinds of urban knowledge? And how could urban science help support understanding of urban fields including the built environment?