Folk perceptions of language diversity often differ from the criteria laid out by linguists and have particular implications for applied/sociolinguists since the collective identification of language diversity largely determines the ways in which individuals regard the categorisation of their own (and others) linguistic uses as belonging to a specific social and/or regional variety. Folk perceptions can thus help define speech communities as well as explain sociolinguistic other phenomena. This paper provides a critical analysis of the existing folk linguistic research into language variation in a number of different contexts: the UK, the USA, France and Japan. It is hoped that the information gained will help build up a more detailed sociolinguistic picture of the complex and often contradictory nature of lay individuals' attitudes towards linguistic variation. In the final sections of the paper the authors argue for a greater deal of recognition within modern linguistics of the value of examining folk perceptions of language diversity.