Bridge from classical to quantum theory of open systems

The paper provides a short survey of some results concerning the physical interpretation of the basic equations for quantum open systems. The concept of a continuous medium for quantum systems is introduced. From this point of view the question of the completeness of description and of hidden parameters (scales) for quantum open systems is considered. The Heisenberg uncertainty principle in the physics of open quantum systems is presented. The question: is the concept of "pure ensemble" justified in quantum mechanics" is also discussed.