This essay looks at the theoretical meaning and practical implications of a much used and abused notion in urban planning and development circles, that of ‘informal settlements. In Mumbai, alone over seven million people supposedly live in them. Yet, what is ‘informal’ about these settlements is not all that clear, especially in the broader context of a city where land tenure and occupancy rights have been historically contested across the housing spectrum. Besides, from an architectural, urban planning, and development point of view, the notion that habitats can be ‘informal’ evokes imaginaries of both crisis – implying the need for urgent and radical action, and anti-conformism – which explains the appeal that ‘informal settlements’ have for design students and scriptwriters alike. After reviewing classic literature on informality, focusing notably on Keith Hart’s original conceptualization of the ‘informal economy and the way it slipped into the more vague and confused notion of the ‘informal sector and from there went to define entire settlements, I propose a few alternative concepts such as ‘enformality’, ‘homegrown neighborhoods’, ‘neighborhoods in-formation and the ‘tool-house’, all based on observations of so-called ‘informal settlements in Mumbai.