In this introductory chapter to the Research Handbook on Development and the Informal Economy, the scientific editor of the Handbook outlines why revisiting the informal economy is timely: the widespread use of the concept in various contexts together with common misconceptions and misunderstandings, especially regarding the relation of the concept to illegality; the availability of measures and estimates for an increasing number of countries and for various periods of time; the moving frontiers of the concept; and finally the diversity of ad hoc policies on the agenda of a number of developing countries. The Handbook addresses the issues of definitions and methods of measurement, assesses the magnitude and trends of the phenomenon, and discusses the strategies and policies designed to tackle it. Informality is a flexible concept, and new frontiers of the concept have emerged that deserve more attention, in particular its extension to unpaid domestic and care work. The Handbook also deals with the dialectics of observation and action on three vulnerable groups of workers in the informal economy, from the most visible because working in the open sun yet also the least known – the street vendors – to the equally visible yet the least regarded – the waste pickers – and finally to the most invisible and equally ignored – the home-based workers. Concrete experiences across the developing world are mobilised to showcase the modalities of organising and giving voice and visibility to these informal workers at the bottom of the pyramid. Finally, the Handbook addresses issues such as the recognition of skills acquired in the informal sector, the role of apprenticeship, and innovation as a potential step towards bottom-up industrialisation or as a means for self-reliance in refugee economies. It also attempts to assess the impact of technological change on the alleviation of women’s burden of unpaid domestic and care work, or as a means for widening the benefits or loosening the clamps of the poor informal workers at the bottom of global supply chains, or also concerning the transformation of home-based piece workers into even more fragmented task- or click workers throughout the digitisation process. This research handbook does not pretend to cover all topics and issues related to the informal economy. The scientific editor’s decision has been to provide a wide and diversified range of approaches likely to make scholars and researchers aware of the issues to be tackled and the challenges at stake within this rather recent field of knowledge in economics and the social sciences at large. It offers historical, theoretical, political and practical entries into a still-burgeoning and debated field of research. It provides some indications or orientations towards domains that require more in-depth investigations, and it paves the way for an improvement of the living and working conditions of informal workers and a renewed discussion about the social contract between the ‘excluded’ and the state.