Automatic continuous online monitoring and control of polymerization (ACOMP) is a widely applicable platform for monitoring and controlling polymerization reactions. It relies on the continuous extraction, dilution, and conditioning of a small sample stream from the reactor on which measurements by various combinations of detectors are made. By combining simultaneous data from multiple detectors continuous monitoring of salient reaction characteristics can be made, such as kinetics, conversion of comonomers, composition drift, evolution of molecular mass and intrinsic viscosity, and detection of unusual phenomena, such as microgelation and runaway reactions. A growing area for ACOMP is its integration into predictive and closed‐loop reaction control with intriguing possibilities for enhancement by machine learning and artificial intelligence. Typical detectors include light scattering (LS), ultraviolet (UV)/visible spectrophotometry, viscometry, refractivity, and polarimetry, while NMR, dynamic light scattering (DLS), Mie scattering, conductivity, and near infrared (IR) and Fourier‐transform infrared (FTIR) are also used. Recent additions to ACOMP include the ability to use multiple similar sensors to detect the onset and evolution of polymer stimuli responsive behavior during synthesis; for example copolymer compositions at which a lower critical solution temperature (LCST) occurs. ACOMP has been applied to free radical, controlled free radical, and condensation reactions, to micellar, emulsion, and inverse emulsion polymerization, to post‐polymerization and derivatization reactions, and to batch, semi‐batch, and continuous reactors. While ACOMP is not inherently a chromatographic method, its continuous stream can be used in automatic conjunction with gel permeation and other separation chromatographies. Recently, ACOMP has been deployed in full‐scale industrial polymerization reactors to optimize efficiency and product quality.