If informality has been conventionally understood as a territorial formation or as a labour categorisation, this paper offers an alternative conceptualisation that conceives informality and formality as forms of practice. The paper examines how different relations of informal and formal practice enable urban planning, development and politics, and explores the changing relationship between informality and formality over time. To illustrate the political potential of conceiving informality and formality as practices, it highlights the fall-out from a particular urban crisis: the 2005 Mumbai monsoon floods. In the final section, the paper offers three conceptual frames for charting the changing relations of informal and formal practices: speculation, composition, and bricolage.