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The four major microwave ferrite devices, ie., the Faraday rotator, the resonance isolator, the nonreciprocal phase shifter, and the field displacement devices are discussed in terms of their loss properties over a range of frequencies. By means of perturbation theory the figure of merit of these devices is derived in the idealized limits for various ferrite geometries. These limiting values are analyzed in terms of the experimental results of the resonance loss for polycrystalline and single crystal measurements and compared with existing data on practical devices. The analysis indicates a possible low-frequency limit of Faraday and nonreciprocal phase shift circulators at about 1000 mc. The low-frequency limit of the resonance isolator is estimated at about 200 mc with a reverse-to-forward ratio of about 10. The problem of broad banding is also discussed in terms of the perturbation results.