Urban environments are complex, impacting on climate change, social justice and health globally and locally. Their spatial, social, economic, environmental dimensions are interlinked and must be studied from a complexity viewpoint. Yet, whilst complexity has successfully entered urban scholarship and practice in many fields, urban form, a key component of urban environments, is not yet studied in these terms and consequently they are not yet designed as complex. This paper argues that the discipline of urban design should be (re)defined as the understanding and design of urban environments as places of organised complexity. It can become the discipline best placed to manage a useful global overview of sustainable placemaking. It does so by tracing urban design's historical relationships and attitudes towards the evolution of the city, contrasting definitions of complexity in science, with the deterministic way in which the early urban design practitioners viewed design. It then looks at urban design's relationship with other design professions in the UK and suggest its lack of clarity and efficiency is an enduring consequence of this historic trajectory. Finally, it proposes urban design as the discipline concerned with the understanding and design of complex-adaptive urban environments and advocate its establishment as an independent profession.