In this article, we outline the development and validation of an instrument for the assessment of attitudes towards religious diversity. The instrument uses four parallel scales, which evaluate attitudes towards Muslims, Christians, Jews and towards Non-religious people. Each scale is subdivided into eight parallel profile types and tests for the acceptance of six levels of social proximity. Drawing on a sample of 281 respondents (which include Muslims, Christians, Jews, Non-religious and Other) and employing the item response theory, we examine the reliability and validity of the instrument and present first results. We found that respondents discriminated greatly between the eight profile types and made clear distinctions with regard to the proximity of social relationships. Relative to these distinctions within each religion, differences between the four groups Muslims, Christians, Jews and Non-religious appeared minimal. These findings suggest that the results of previous research which indicate scepticism towards Islam despite general respect for religious diversity could be due to stereotyping.