This paper presents a review of the various applications of feedback in optical systems. There are two general areas, optical image processing and bistability. In optical image processing both coherent (optical spatial feedback network internal to an optical resonator) and hybrid (TV) systems are discussed. In the area of bistability there are molecular systems (atoms in an optical resonator), both absorptive and dispersive; hybrid (employing electronic feedback) single-beam and many-element (TV and spatial light modulator-based) systems. All the systems are discussed. A detailed model showing the many facets of molecular bistability is presented along with a discussion of catastrophe theory applied to optical bistability.