Urban Informality and the Built Environment: Infrastructure, Exchange and Image argues that urban informality should not be understood only through legality, state regulation or poverty, but through the built environment as an active producer of social, political and economic relations. The book challenges state-centred readings that define informality as what lies outside planning or law, and instead proposes a relational approach based on infrastructure, exchange and image. Infrastructure is not limited to roads, pipes or services, but includes social, cultural and visual systems through which people organise urban life. Exchange refers to the everyday practices that produce space: markets, water systems, welfare networks, artistic interventions, care economies and local forms of cooperation. Image concerns how informal spaces are seen, represented and judged, warning against both the romanticisation of poverty and the erasure of local urban intelligence. Through case studies from Accra, Galicia, Tirana, Athens, Havana, Taipei and Mumbai, the volume shows that informality is not marginal to the city; it is one of the ways the city is made. Graffiti in Accra, collective water infrastructures in Galicia, informal welfare spaces in Athens, urban agriculture in Havana and children’s mapping in Mumbai reveal how inhabitants transform space through situated knowledge and material invention. These examples question fixed oppositions such as formal/informal, planned/unplanned, legal/illegal and centre/periphery. The book’s main contribution is methodological and political: it asks architecture, planning and urban studies to foreground materiality, morphology, aesthetics and positionality. Informality becomes a lens for understanding power, inequality, creativity and urban reproduction, rather than a residual category of urban disorder. Instead of offering a universal definition, the book proposes a plural framework attentive to context, voice and embodied spatial practice. Its conclusion is that studying informality through the built environment can help decolonise urban knowledge and open more precise ways of addressing urban injustice.