The paper describes the history  of the Q-system that was introduced in 1974, and its later development. The individual parameters are analysed, and their relevance for the natural geological features they seek to simulate, is discussed. It is concluded that the Q-system, used with full awareness of its limitations, may be applied for classification of the stability and support estimates of tunnels and rock caverns, preferably in jointed rocks. Applied here, it may be used  for planning purposes. It  is less useful for prescription of rock support during construction.