During the nineteenth century a long-run trend towards increasing functional and geographical specialisation of non-residential property emerged, and accelerated during the twentieth century, creating the functionally segregated built environments of modern urban centres. This chapter examines the evolution of commercial and industrial premises from around 1840 to the 1950s, together with associated changes in the property investment and development sectors and the building industry. Over the century to 1914 the diversity and specialisation of Britain's urban built environment had increased enormously, though the pace of change was to accelerate further after the First World War. The interwar period saw important changes in the character of Britain's commercial property sector. The development of motorised transport encouraged both an intensification of specialisation within urban centres and the suburbanisation of residential and industrial buildings. The onset of the Second World War led to a virtual halt in property market activity and a severe fall in commercial property values, particularly in London.