Abstract‘Cities need to change to survive. As living beings that are constantly replacing their cells, rebuilding their veins and arteries, and pumping energy and matter or producing waste, cities are also growing and evolving as they age.’ Just how complex, though, are cities? Sergi Valverde and Ricard V Solé of the ICREA‐Complex Systems Lab at the Universitat Pompeu Fabra in Barcelona look at how network theory and emergent dynamics might be bringing us closer to an overarching theory of urban organisation.