A review of the authors' work on orthogonal polarization of optical feedback in He–Ne and microchip Nd:YAG lasers is presented. Orthogonally polarized optical feedback has been applied to dual-frequency lasers and to monomode lasers with birefringent external cavity. The greatest advantage of the technique is that two modulated beams can be obtained with only one optical feedback path, so more information can be obtained than with conventional optical feedback. Polarization flipping with hysteresis and intensity transfer between the two eigenstates of the laser, the characteristics of intensity tuning, subdivision of the laser emission bandwidth, the phase relationship of the two orthogonally polarized intensity modulation curves, mode competition, signal frequency doubling through optical feedback, measurement of the small intracavity phase anisotropy in lasers, and antiphase intensity modulation of orthogonal polarization are experimentally and theoretically demonstrated. Possible applications are also discussed.