Social requirements concerning experts with complete secondary education are reflected both in the content and in the organisation and administration of the educational process as well as in the system of study branches at Secondary Vocational Schools. The development of the system of study branches is a complex process, which is influenced by a number of factors, but especially: 1. by the national economy and the speed of its development in each of its sectors, 2. by the educational system and the secondary vocational school system as one of its components and 3. by tradition. The first of these factors has an accelerating influence on the development of the system of study branches while the other two factors have a retarding influence. The retarding factors of the development of the system of study branches have a significant stabilising function. In the development of the system of study branches there are two principal tendencies operating against each other: we can observe on the hand a horizontal differentiation and on the other hand the tendency to integrate study b ranches so as to form study branches of a broad professional profile, with both these tendencies reflecting the requirements of social practice. They reflect the operation of social requirements of a different character: objective nation-wide requirements, and immediate social practice in individual branches of the national economy. In the advanced socialist societies the trend of the development of the system of study branches is towards the formation of study branches of a broad professional profile. The mechanisms of the dynamism of the system of study branches are mostly known nowadays, but a number of important questions still remains unanswered.