The opinion that performance of continuous catalytic processes under invariable conditions is highly efficient has gained great popularity, especially among chemical engineers. However, very often the optimal conditions of the process can be achieved with the so-called unsteady-state operation. The steady-state condition thus appears to be a particular case of the variety of unsteady-state conditions which can be obtained, e.g., by changing the reaction conditions. Unsteady-state operation opens up wide possibilities to form the profiles of the catalyst states, concentrations, and temperatures in reactors, thus providing more favorable conditions for the process performance.