The present article summarizes the fundamental principles and recent advances in free radical polymerization systems. Each individual reaction step in the polymerization process—initiation, propagation, transfer, and termination—is discussed in detail with regard to the underlying first principles and to the latest rate coefficient data. Novel methodologies, including living free radical polymerization, are also introduced within this context. In addition, the article gives an up‐to‐date overview of current state‐of‐the‐art experimental techniques for obtaining reliable kinetic and mechanistic information, embedded in an extensive coverage of the rates of radical polymerization, thermodynamics, and the chain‐length distribution. Such techniques range from now quasi‐classic experiments, such as pulsed laser polymerization, size exclusion chromatography, and the chain‐length distribution method for transfer constant determination, to cutting edge methodologies, such as the use of living free radical processes for chain‐length‐dependent rate coefficient determination. The fundamental differential equations governing free‐radical polymerization and the chemistry involved are both extensively covered along with ample tabular material, giving the practicing polymer chemist up‐to‐date and easily accessible data material backed up by over 500 references.