This article aims to synthesize and analyse one of the most relevant bibliographic sources emerged in recent years, which has the object of study debates on very controversial phenomenon of inequality. Place, role and impact of social class on social stratification system has been and continues to be a subject of study for researchers coming from different traditions of thought. The survey shows the persistence of different approaches and methodologies for the identification, evaluation criteria and measuring social classes, with special attention being paid to the middle class. The analysis results show a demand for comparative studies at national, regional and international problem of inequality.