This paper aims to inform marketers and researchers interested in Mexico's market about how the Mexican Association of Research and Public Opinion Agencies (AMAI) has dealt with the problem of defining a common ground where all parties involved (research, advertising and media agencies, along with advertisers) talk the same language in terms of socio-economic levels. Additionally the paper aims to make a brief comparison among the SEL classifying systems used in the three main economies of the Latin American world in order to provide a first approach to what could in the near future become a simple rule of 'comparability' among the three systems. This idea does not mean, at this moment, to create a unique classifying system for the three countries. On the contrary its aim is to look for ways in which the outcomes of the already developed statistical models for classifying households could be more comparable. Nevertheless, in the future a common system should be jointly created by the professional research associations involved.