Pertains to ferroresonant voltage regulators that operate at relatively constant frequencies and provide substantially constant output voltages in spite of relatively large changes of input voltage, and to controlled ferroresonant regulators which maintain substantially constant output voltage regardless of variations, within limits, of input voltage, temperature, frequency and output load. Guides to application and test procedures are included. Provision is made for relating the rectifiers and circuits. Definitions pertaining to ferroresonance and ferroresonant regulators that have not been found elsewhere are included with an appropriate discussion.