A theory regarding vocational schools as a coherent system of statements that can rely on empirically validated knowledge, or that helps to organize this knowledge and, on this basis, make predictions about the effects of political measures in vocational schools, is not yet available. The fundamental idea of the analyses presented here is that a theory development in this direction would initially require a categorical basis that allows for an appropriate description of the object area. The analyses refer to two levels, beginning with systematizations of the object area. The author distinguishes between the institution of vocational education (entitlements, curricula, state legitimacy contexts) and the organization of individual schools (structural, administrative, and legal organization), outlining the interactions between the institution and organization of vocational schools. Fundamental categories for describing the object area of vocational schools are developed. Based on this, deficiencies in the performance of theory approaches related to the object area are analyzed.