Cities are getting interested in education and learning. Urban planners, geographers, international agencies, and city leaders are beginning to adopt a language of 'learning' and 'education' to try to make sense of how cities and their inhabitants might adapt to contemporary challenges from economic inequality to sustainability. There are now international networks of 'Smart Cities' and calls for 'Wisdom Cities' (Hambleton, 2014); there are networks in which policymakers, industrial partners, and academics who see the city as a 'laboratory' share information about experimental learning; 1 and above all there is the longstanding (dating back to at least 1972) aspiration amongst an international network of cities to be recognised as 'Education' or 'Learning Cities' in which schools, universities, workplaces, and civil society work together to promote learning across the life-course. From one perspective, of course, it is possible to dismiss such developments simply as another in the long list of Brownie badges that cities increasingly accrue to promote themselves in competition with each other-alongside badges for 'resilient cities', 'happy cities', and so forth. From another, this increased attention to learning as central to the formation of viable cities, generating investment, policy action, and producing real effects on the ground, merits critical scrutiny. This Special Issue on Learning Cities aims to begin that process. In this extended introduction, we explore the nature of the inquiry that might be adequate to dealing with the complex interconnections between space, place, policy, education, culture, materiality, and technology that are necessarily engaged when learning becomes a focus of attention at the scale of the city. What is a city? Why would 'cities' be interested in learning? A city can be understood, in Brenner and Schmid's (2015) terms, as a theoretical rather than an empirical category. A city does not, in any empirical sense 'exist' independently of the flows of people, resources, and information that connect it to the countryside, towns, to other cities, to informational resources and governance structures that constrain and enable its existence. To call something a city is an ideological act that draws boundaries that cannot contain empirical reality. Instead of conceptualising a city as some sort of 'container' or 'organisation', then, we might be better to think of cities as 'relational entities' (Amin, 2007) or dynamic processes (Brenner & Schmid, 2015) as 'gatherings' and 'assemblages' of human, material, and discursive elements that are both relatively stable and constantly changing (Amin & Thrift, 2002). A city then, is more verb than noun, an ongoing discursive and material process characterised by complexity