The concept of “formal” equality is an expression of the Aristotelian principle that “treats like cases as like”. However, formal equality may not be sufficient to provide “equality in practice” or “substantive equality.” The implementation of substantive equality often requires the adoption of compensatory policies or measures designed to correct the effects of discrimination suffered by various population groups in the past or present. Such compensatory measures are known as affirmative or positive action. The term “affirmative action” had its beginnings in the 1960s in the USA, as a response to the racial segregation rooted in the country’s history and still prevalent in that decade. In the European Union, the concept of positive action appeared in the 1970s, and was initially associated with promoting gender equality, and subsequently with “substantive” equality of men and women in the workplace. In this chapter the legislative framework and the case law of the Supreme Court is examined in respect to affirmative action in the United States followed by the corresponding European Union legislation and the case law of the ECJ, attempting, finally, to give a comparative review of the law of affirmative action. This study should help us, through the spectrum of Comparative Law, to better understand not only the concept of social rights but also the different values and different perceptions of the law prevailing in different legal cultures.