What defines certain transformations of urban spaces as ‘temporary’ or ‘tactical’, and what gives them fresh validity and value? This chapter draws upon Assemblage Thinking and Actor-Network Theory to focus on the role of temporariness in shaping urban development. It explores time in relation to the production and use of the urban environment. It shows how temporariness defines and enables specific relationships to the many actors and forces that shape cities. Before, during and after ‘temporary use’ people, money, regulations and materials are won over to it. Temporariness avoids and withstands challenges; it adapts. These dynamics are explored in terms of various benefits and impacts that temporary urbanism can have for other actors and longer-lasting forms of urban development. This characterisation of temporary urbanism and its networks of interdependence link it to wider critiques of neoliberalism, modernist masterplanning, and historic preservation. This examination of today’s temporary urbanism highlights two paradoxical dynamics that constantly influence the form of cities. Firstly, temporary urbanism, for all its claimed ephemerality, constantly establishes new, durable relationships and has broad and enduring effects. Secondly, all urban spaces aremore-or-less impermanent assemblages of materials which are constantly being adjusted to meet changing resources and needs.<p></p>