The present study reports the averaged IQ scores in 21 European countries, collected during a period exceeding five years. An attempt was made to test a representative sample in all European capitals. It proved possible to do this in 16 capital cities, but in five countries it was necessary to choose the biggest or the second biggest town instead of the capital (Amsterdam, Bratislava, Hamburg, Zagreb and Zurich), the assumption being made that these cities would represent the whole country in a meaningful manner permitting of suitable comparisons to be made. Participants of the study were men and women of 16 years or more, the assumption being made that the development of intelligence in most cases would be completed by that age. The scale used was Cattell’s Scale CFT3, a non-verbal, culture-fair test which is particularly appropriate for comparisons of different nationalities. The test has high g saturations and is a good measure of general mental capacity, particularly fluid general ability (Weiss, 1971). The test was validated and standardized in the United States, and all comparisons are with the standardization figures. The sample was based on the testing of one person for each 40,000 inhabitants, and the sample may be considered as stratified because three subgroups of the population were represented proportionally: (1) Men and women; (2) Age of participants (distribution was into six classes, beginning with the 1620 year olds, and then going up by 10 year steps to the over 60s); (3) Socio-economic status was also considered, using a threefold classification. Probands were ascertained by the investigators through the use of population statistics, and were then tested in groups of about 50 persons, The investigations were carried out by qualified psychologists and students of psychology who were carefully instructed to use identical criteria of testing. In each case the experimenters were of course native born in the country in question. For all sampling purposes the breakdown was based on the total population of the country, not on the particular town or city in which the test was carried out. Altogether 10,737 persons were tested. Results are shown in Table 1, which gives the number of persons tested In each City, the mean IQ value, the standard deviation, and the standard error. The arithmetic mean for the total population tested was 102.2, with a standard deviation of 18.7. The population was 48.8% male and 51.2% female.