The principles of ferromagnetic resonance have been well described in literature. It is the purpose of this paper to point out the application of these principles to the design of practical microwave components, especially for high power. The various types of ferrite microwave circuits that can be used in the design of a load isolator are presented. The advantages and disadvantages of each of these circuits are discussed in regard to the electrical, mechanical, thermal, and magnetic field requirements. Experimental data are given for the optimum design of nonreciprocal ferrite absorbers for rectangular guide. Finally, practical design information for a power circulator in rectangular waveguide is presented which has been modified for use as a load isolator. This device has extremely high isolations (50 db) and low insertion loss (.5 db), and has maintained an isolation in excess of 30 db over a 25 per cent bandwidth with a permanent magnet field. Power handling ability of 250 kw peak with a .001 duty cycle is easily accomplished without external cooling. This isolator requires quite small magnetic fields for proper operations and hence packaged isolator is quite lightweight. Use of this power circulator for high-power modulators and duplexers is discussed.