It was initiated in the summer of 1985, when there was renewed concern that increasing numbers of experienced scientists and engineers were leaving the UK to work abroad. The study aimed to collect quantitative evidence about such emigration and the extent of any similar flow of foreign scientists and engineers to the UK. It became increasingly evident during the study that a proper assessment of the impact of migration depended as much on the quality of migrants as on their number, although quality is clearly more difficult to measure.