Drawing on years working in the squatter settlements of Peru, the architect John F. C. Turner argued in Freedom to Build (1972) and Housing by People (1976) that housing works best when residents control its design, construction and management. He challenged the demolition of informal settlements, contending that self-built housing improves incrementally and meets needs better than imposed public projects. Distinguishing housing as a verb, an ongoing process, from housing as a finished product, his ideas influenced international agencies toward supporting rather than clearing informal urbanism.
It reshaped global housing policy toward site-and-services and slum upgrading rather than mass clearance, recognising self-built urbanism as a resource. Turner's work legitimised the informal city as a subject for planning rather than simply a problem to remove.