A pioneer of the market research industry, founded in Chicago in 1923 by Arthur C Nielsen. The main expertise is in consumer marketing and media research. It opened in the UK in 1939 and more widely in Europe and Asia after 1945. The company now operates in 100 countries. Nielsen was an early leader in measuring the impact of marketing investments, for example in market share and the ‘Nielsen Ratings’ which measure television, radio, and newspaper audiences.