Social Stratification and Social mobility were included among Geiger's main interests and within these subfields, he made several contributions to sociology. His interest in social stratification began in the 1920s when he initially accepted the Marxist definition of class. However, Geiger quickly developed his own definition of class and several theories on the subject. In his 1930 publication (On the Theory of the Class Concept and the Proletarian Class), he distinguished his view from the Marxist concept that class structure is entirely determined by ownership of the means of production. Geiger argued that the Marxist ideology of class was a decent generalization but that it was also a "type concept" and described only a partial view of reality. Further, he felt that the Marxist Two-class model was an accurate description of the earliest forms of capitalism but that modern developments did not fulfill Marx's predictions of the polarization of classes and intensified class conflict. He believed society to be dynamic, so although he agreed with Marx, he believed that there are other causes and types of stratification other than those of the narrow Marxist definition and concept. Instead, he looked at the classes of society in terms of stages, with estate society preceding the class conflict of Geiger's present, and a new stage to come in which society will form into distinct, specific social groups. He also acknowledged income, level of education, and political power as new factors for stratification. Geiger developed a complex model and typology of social stratification, which was published in Wörterbuch der Soziologie (1955). In many ways, Geiger defended Marxism but he also agreed with arguments that many predictions made by Marxist class theory were not carried out.