Equality can—along with freedom—be considered a central societal value that has long been recognized and pursued as such. As an introduction to the discussion of this concept, six theses are put forward: They concern the complexity of the concept of equality, the value of inequality, the differentiation between two fundamental forms of inequality, the persistence of inequality, the frequent equation of equality and justice, and the political relevance of the concept of equality. The modern concept of equality has its origins in the historically unique social structure and society of ancient Greece, as well as in Christianity and the peasant wars in the early modern period. Since then, the idea of equality has been systematically formulated in four variants: in the bourgeois-liberal, the radical-revolutionary, the conservative-estates, and the democratic-reformist concept of equality. A distinction is then made between total inequality and group-related, specific forms of inequality: the former existed in the form of slavery, estate society, and gender inequality; the latter refer to specific groups such as disabled people, immigrants, and non-citizens, and also to women. Finally, the important distinction between procedural and distributive inequalities is highlighted: the former concern the assignment to educational opportunities and professional positions, the latter the inequalities in income and wealth. In each of these forms, attention must be paid to processes if one also wants to identify aspects of disadvantage and injustice in them.