The service sector, since 1970, has increased from 53 per cent of the economy to 74 per cent today. It is now by far the largest and fastest changing sector of the UK economy. This article describes the significant improvements that the Index of Services (IoS) development programme has brought to the measurement of the output of the service sector, as well as the output measure of gross domestic product. The article also plots the journey of the IoS from its launch in December 2000 as an experimental statistic to its expected reclassification on 29 March 2007 as a National Statistic.