Optical correlators (OCs) have received much attention since VanderLugt’s invention in the mid-1960s, when he showed that pattern recognition can be optically realized using matched spatial filtering techniques. The classical VanderLugt correlator used photographic plates or film for carrying both pieces of information: the input and the reference, in the form of a matched spatial filter. Thus, early applications were limited to rather simple problems such as character (shape) recognition or fingerprint identification. Later applications include more sophisticated approaches due to the developments in addressable spatial light modulators, in designing the correlation filters, and due to the versatility of the correlator system configurations. Desirable performance properties of OC devices generally include high-discrimination ability, high speed, and robustness to noise and distortions. Here, the OC applications are reviewed according to the following sections: early perceived usage, distortion-invariant systems, real-time or large capacity systems, various system solutions, and user oriented devices.