Magnetorheological fluid (MRF), due to its controllability under a magnetic field, can be used as a base of new devices and technologies. The most important element of any MR device is a magnetorheological converter (MRC) being functionally a controllable hydraulic resistance. Its mathematical model is obtained using quasistationary approximation. A method of description of the dampers and shock absorbers is given, as well as the actuators with a flexible bridge-like distributor. The possibility and advantages of seals with MRF as a working medium are shown.