During the last decade, it has been established that conventional mineral- processing control strategies based on classical control theory result in significant increases in plant throughput and operating-cost saving. The proper education and training of personnel using dynamic simulators of the principal unit operations is vital for proper design and maintenance of control systems. Severe multivariable interactions and numerous constraints on both manipulated and state variables in grinding/classifica- tion and flotation systems can be studied using time domain analysis with proper dynamic simulators. Two interactive programs are described, and the basis of each simulator and its structure are discussed. Two examples concerned with choosing, tuning, and decoupl- ing of manipulated and controlled variables for a grinding/classification circuit (DYNA- MILL II) and for a rougher flotation circuit (DYNAFLOAT II) are presented. The way in which these dynamic simulators can be used for the design of model-based control strate- gies is also outlined. A brief description of the use of these dynamic simulators for screening alternative strategies and circuit optimization is given.