The characteristic features of deterministic and nondeterministic optical threshold logic gates are reviewed. Analog, binary, multiple-valued, multiple-class, and polynomial threshold gates are considered. Threshold synthesis techniques are outlined. Bulk optical and integrated optical implementations of reconfigurable threshold gates are discussed. Examples of deterministic logic operations involving binary addition and digital picture processing are presented. Applications to nondeterministic operations such as pattern recognition and heteroassociative processing are considered. The sensitivity of deterministic and nondeterministic mul-tiple-input optical threshold gates to physical errors is analyzed. The particular advantages of optically connected threshold gates with respect to electronic threshold gates are discussed.