The mature welfare states of high-income countries face increasing social instabilities and challenges to ensuring basic economic security for all wage earners. It is therefore a germane time to ask: how do welfare states protect workers against financial insecurity? What drives governments’ policy choices in this area? Within this sphere, a key reform trend since the 1990s is the objective of ‘making work pay’ (MWP) and the implementation of in-work benefits (IWBs) in many countries. Yet, why might governments choose for the state to directly subsidise workers’ earnings rather than relying only on higher wages, tax cuts or more traditional social benefits? To address these questions, the monograph studies in-work benefit and wider ‘making work pay’ reform trajectories in France and the UK since the 1990s. This introductory chapter outlines the book’s policy context, case studies, theoretical issues and research design.