This paper examines how measurement problems affect international comparisons of labour productivity. It suggests that these measurement problems do not significantly affect the assessment of aggregate productivity patterns in the OECD area. However, these problems do influence the more detailed assessment of productivity growth, notably the role of specific sectors and demand components in aggregate performance. The paper shows that there are only a few significant problems regarding the comparability of nominal GDP across OECD countries, the most important being the treatment of software investment. In most cases, efforts are underway to reduce the size of these differences. Measurement differences for real GDP are also important, although several of these factors have impacts that work in different directions. Moreover, several of these problems primarily affect the distribution of total GDP across different expenditure categories and across different activities, not necessarily ...