The structural rate of unemployment and associated non-accelerating inflation rate of unemployment (the NAIRU) are of major importance to the analysis of macro and structural economic developments, although in practice these concepts are not well defined and there is considerable uncertainty and controversy concerning their measurement and policy use. The present paper reviews a range of conceptual and analytical issues and related empirical studies to examine the usefulness and limitations of such concepts. A reduced-form Phillips curve approach is found the most suitable conceptual framework for representing the NAIRU as currently used by the OECD in its policy analysis and surveillance work. Three distinct classes of NAIRU concept are identified, distinguished by the time-frame in which they are defined, which map directly into the broad requirements for macro and structural policy analysis. In line with a number of recent empirical studies, this general approach is applied ...