This paper lays out the basic theory behind productivity measurement, whether at the level of the country, region, industry or firm. The theory is illustrated using recent data from UK official publications. Productivity growth over time and differences in productivity levels between countries or regions at a point in time are both covered. Labour productivity and multi-factor productivity (MFP) are discussed. In the case of MFP special attention is paid to the measurement of capital inputs. Wherever possible, an accompanying spreadsheet supplies data from recent publications by the United Kingdom’s Office for National Statistics so that readers can reproduce official estimates or even employ alternative assumptions to produce their own estimates. Limitations in the underlying theory are highlighted as are empirical difficulties in implementing the theory.