"The overall aim of this paper is to outline a review of the concept of usefulness. In particular, it looks at the facets of usefulness and the methods and tools that could help to develop a useful system from the perspective of ergonomics. First, we present the research context and explain our motivations for focusing on the usefulness of innovative systems. One reason is that there is no theoretical or methodological framework that explicitly addresses usefulness as a guide to design and define goals, in contrast with the concept of usability. The first section aims to clarify the concept of usefulness. We have highlighted two dimensions of usefulness: purpose-usefulness and value-usefulness. Purpose-usefulness relates to the functional and non-functional features of the artefact. Value-usefulness relates to the improvements or significant benefits that the artefact can bring to users. We then clarify the relationship between usefulness and requirements. The requirement is the original inspiration, the argument and the justification associated with the usefulness of an artefact during the design process. The second section presents usefulness from the point of view of ergonomics. First, we show the extent to which usefulness is a built and progressive feature of systems by revealing two worlds of usefulness: the prospective world and the retrospective world. The prospective world gathers all features, requirements and thinkable (although not necessarily desirable) solutions; the retrospective world puts together all the relevant experiences in terms of usefulness to inform designers of the artefact. We then specify the relationship between usefulness and other criteria of ergonomics, such as usability or acceptability. The third section provides an overview of methods and their contributions to the different facets of usefulness. We detail the contribution of methods to the production of a hypothesis and the development of prospective worlds, before moving on to prioritization, selection and the decision-making process. Finally, we examine the evaluation of usefulness. In this part, we discuss the links between the more or less conscious nature of the requirements, the two dimensions and the two worlds of usefulness. Our conclusion includes the most relevant elements for the clarification of what is underlying the concept of usefulness in the context of the design of emerging technologies."