Curricula prescribing the subjects of study for education and training have existed in their current form and significance since the 16th century. In the Middle Ages, the "septem artes liberales" (Mediaeval Schools ) prescribed the framework for teaching. In the modern era, instruction gradually became prescribed by an "Ordo docendi", the schools were normed, and teachers were obliged to adhere to these norms. These norms or "Schulordnungen" were set down at first by the headmasters of the schools, soon after by the secular and religious authorities, and from the 18th century by the state, always taking advantage of directive and motivational possibilities. The increase in the volume of knowledge and the demands of society have led to a differentiated school system with numerous subjects of instruction and increasingly detailed new curricula at increasingly shorter intervals. The current curricula include: 1) the overall educational goals, the educational objectives of the individual subjects of instruction, and didactic principles; 2) the division of the subject matter among the various school levels; 3) the total number of hours of instruction and the number of hours to be devoted to each subject. They also stipulate which subjects are compulsory, which are required electives, and which are optional graded or non-graded supplementary subjects. The curricula are, without exception, oriented towards educational objectives and ensure that the teachers have leeway with regard to emphasis and method, although they are required to present the material according to the latest academic insights and at the same time in a clear and understandable manner which takes into consideration the level of development of the pupils and maintains relevance to the present time. They are also expected to aim for an overall educational effect in all subjects, encourage their pupils to develop independence, participate in the group, and achieve performance levels corresponding to their individual abilities, as well as reinforce instruction through appropriate exercises.