This is a reference book on ergonomic intervention methodology. What makes it distinctive is its focus on the actual intervention process, the “how to” of ergonomics in action. Although it also lays out the theoretical foundations, its primary goal is to formalize what Quebec researchers and practitioners do to transform work situations with respect to current issues (musculoskeletal disorders [MSDs], lean production systems, service relationships, etc.). The book gives English-speaking readers a unique opportunity to learn about the concepts and methods of ergonomic intervention in the French-speaking world, as they have been adapted to the Quebec context, which lies on the boundary between the French-speaking and English-speaking ways of doing things. The approach described revolves around activity analysis, a concept that has been extensively formalized by French ergonomists. It is quite different from an approach that concentrates on applying standards or solely on analysing risk factors. Part I of the book is devoted to the theoretical foundations of ergonomic intervention. The first chapter sets out a model of the work situation focusing on the individual. This provides a basis for work activity analysis. The second chapter describes an intervention model that outlines the various stages of ergonomic intervention. Part II forms the core of the book. Each chapter examines a specific stage in the ergonomic intervention process: analysis of the intervention request, initial investigation, analysis of the work situation, formulation of a preliminary diagnosis, drafting of an action plan, and design of transformation plans. The last chapter deals with cases where further investigation is required to fully understand the work activity. Part III, which is unique for this kind of publication, concentrates on some concrete aspects of an ergonomist’s practice. Based essentially on interviews conducted with practitioners active in a variety of settings, Chapter 9 is devoted to the characteristics of practice, the skills ergonomists must develop and the strategies they use in different contexts. The chapter anchors the book in the realities of everyday ergonomics and offers all kinds of advice and ideas about the work that ergonomists do. To make the book more practical, the appendixes contain a series of tools that ergonomists regularly use: context analysis form, interview questions, investigation questionnaires, logbook, etc. How to carry out an ergonomic intervention is not self-evident. It’s something that has to be learned and that’s the theme of this book: how to analyse actual work activity, develop good design and transformation guidelines, and promote their implementation, taking into account the specific context of each workplace.