Studies of borders and their nature should not ignore those borders defined from within, by specific social groups, through their collective cultures. The analysis presented here aims to examine in particular the invisible boundaries which defined `otherness’ in southern France in the 1920s. This involves considering the dividing lines and the various collective representations that governed relations with `the other’, with foreigners and with migrants. This paper will also consider how `otherness’ was understood and judged in these years when immigration was so important and so widely debated, both at a national level and in the south-west region: more precisely, in those parts of Midi around the city of Toulouse, which will form the principal field of investigation for this study.