Internationally comparable data are essential to our understanding of income inequality and its impact on our societies. The Luxembourg Income Study (LIS) has played a key role in raising to a new level such comparative analysis, and its collection of microdata has been used by a wide range of social scientists. The contribution of LIS over the past 20 years can be seen from the fact that there is now a broadly agreed picture of the differences in income inequality across OECD countries (Section 1). The present importance of LIS lies in the need to keep the picture up to date in a rapidly changing world, and in the sensitivity of analysis to data quality and comparability (Section 2). Looking to the future, it is argued that LIS will continue to be crucial, but that more needs to be done in creating long-run annual time series and in modelling the impact of policy (Section 3).