A review is given of scores on various cognitive measures, comparing groups of ethnic Dutch and non-Western immigrants using a large number of datasets. The research shows that there are large group differences in school results, work proficiency, and g for Turks, Moroccans, Surinamese, Netherlands Antilleans, and Indonesians from the Moluccans compared with ethnic Dutch. However, South-East Asians score higher, and persons with one immigrant and one ethnic Dutch parent score only slightly below the mean of the Dutch. When comparing first-generation disadvantaged immigrant groups with later generations the data show substantial improvements for g, a remarkable stability of educational differences for younger children, and a clear improvement in educational achievement at the end of primary school. Indirect data on intergenerational improvements in work proficiency appear suggestive of a trend of closing gaps. Some of the data reflect higher cognitive capacities over time, and this enhances integration of immigrants into Dutch society. Causes of group differences and improvements in mean level of g are discussed. Copyright © 2004 John Wiley & Sons, Ltd.