When economists, sociologists and psychologists discuss skill they often appear to be talking about different things, even though they each ascribe high importance to it. To make progress and to facilitate inter-disciplinary communication it would be better to be sure what we mean by skill. I propose a simple functional concept that offers the prospect of dialogue and progress in skills analysis. Skills have three key features: they are Productive, Expandable and Social. I advocate this ‘PES’ concept of skill, examine how far the approaches of economics, sociology and psychology conform to it, and compare ‘skill’ with ‘competence’ as widely used in human resource management and in educational discourse. I consider implications from the intimate connection between skill and value, some of which are contradictory. Finally I describe some common typologies of skills and skills mismatches that follow on from the PES concept.