Free-radical polymerizations are carried out in extended ranges of temperature, pressure, and conversion. The precise knowledge of individual rate coefficients of initiation, propagation, termination, and chain-transfer is essential for the modelling and optimization of monomer conversion and of polymer microstructure in technical polymerizations. In addition to the application-oriented interest, this data is of fundamental importance for the detailed understanding of reaction mechanisms of such free-radical-molecule, free-radical-free-radical, and unimolecular decomposition processes. Even for the polymerization of rather common monomers at moderate temperatures and ambient pressure such information is scarce. The present paper illustrates some recent advances in measuring, within wide ranges of pressure and temperature, propagation and termination rate coefficients of free-radical homo- and copolymerizations and also peroxyester decomposition rate coefficients.