Research into the general public's responses to individuals with intellectual disabilities has been dominated by attitudinal research. While this approach has unquestionably generated useful findings, it ignores important aspects, such as lay knowledge, explanatory models and beliefs about suitable interventions that can produce a multi-faceted understanding of public responses. This paper describes the development of a measure designed to assess respondents' intellectual disability literacy. Following a pilot with 114 participants, the IDLS was revised and then completed by 1376 members of the public (aged 18-78 years) from diverse cultural backgrounds. The measure was able to distinguish respondents who showed good intellectual disability literacy. Confirmatory factor analyses revealed four causal beliefs factors (adversity, biomedical, fate, environment) that accounted for 55% of the variance and three intervention beliefs factors (lifestyle, expert help, religion/spiritual,) that explained 52% of the variance. Test-retest reliability for these factors was good for all ethnic groups. The four-item social distance scale had good internal consistency for all ethnic groups and acceptable concurrent validity. The IDLS is a useful new tool to evaluate knowledge, beliefs and social distance to intellectual disability in lay people, is suitable for cross-cultural research and allows comparison of intellectual disability and mental health literacy in any given population. (Contains 9 tables.)