"There has been a marked revival of interest in the study of the distribution of top incomes using tax data. Beginning with the research by Thomas Piketty (2001, 2003) of the long-run distribution of top incomes in France, a succession of studies has constructed top income share time series over the long-run for more than twenty countries to date. These projects have generated a large volume of data, which are intended as a research resource for further analysis. The world top incomes database aims to providing convenient on line access to all the existent series. This is an ongoing endeavour, and we will progressively update the base with new observations, as authors extend the series forwards and backwards"--Introduction.