The period 19l9-1946 is widely regarded as crucial to the developme~t of modern town planning in Britain; it marked the final stage of the transition from an initial concern with suburban housing to the regulation of the physical environment in the interests of the community as a whole. A number of studies have described this transition in overall terms, but comparatively few have focused on specific policy areas and their emerging relationship with land use planning. This thesis examines civil aviation, with particular reference to London's terminal airports, and, by using unpublished material, i.e. correspondence, internal memoranda, and the Minutes of meetings and presented papers, presents an insight into the deliberations behind public pronouncements. The policy for London's terminal airports developed as a result of private initiative and public enterprise, while the role of individuals was often significant - notably Raymond Unwin, Robert Hardy-Syms, Thomas Adams, Frank Hunt, and Alan Cobham. Some fifty sites were considered during the inter-war period including Croydon, Heston,Fairlop, Gatwick, Lullingstone, and Heathrow, although the latter only emerged as a departmental proposal in response to the war-time needs of the RAF. Civil aviation and land use planning developed as separate activities throughout the 1920s, neither recognising the significance of the other. Thereafter, statutory land use planning failed to respond positively to pressures from the growth of air travel, mainly due to the limitations of the institutional framework. The advisory planning bodies of the 1930s, by contrast, put forward original, long-term proposals for airports in the Greater London area; these were not well received by Government departments but they proved influential. An examination of the background to the civil airports proposals of the Greater London Plan (1944), the famous war-time advisory plan, reveals that Patrick Abercrombie merely accommodated the Coalition Government's policy for Heathrow and formulated his road and rail proposals accordingly