Respondents at an Internet website completed over 600,000 Implicit Association Tests (IATs) between October 1998 and April 2000 to measure attitudes toward and stereotypes of social groups (www.yale.edu/implicit). Their responses demonstrated, on average, implicit preference for white over black and young over old, and stereotypic associations linking male with science and career, and female with liberal arts and family. The main purpose was to provide a demonstration site at which respondents could experience their implicit attitudes and stereotypes toward social groups. Nevertheless, the data collected are rich in information regarding the operation of attitudes and stereotypes, most notably the strength of implicit attitudes, the association and dissociation between implicit and explicit attitudes, and the effects of group membership on attitudes and stereotypes.