The IUPAC-sponsored International Symposium on "Radical Polymerization: Kinetics and Mechanism" was held in Il Ciocco (Italia) during the week September 3-8, 2006. It was the fourth within the series of so-called SML conferences, which are the major scientific forum for addressing kinetic and mechanistic aspects of free-radical polymerization and of ontrolled radical polymerization. Top international authors like K. Matyjaszewski, T. P. Davis, T. Fukuda and others present their latest research.The five major themes covered were: Fundamentals of Free-Radical Polymerization, Heterogeneous Polymerization, Controlled Radical Polymerization, Polymer Reaction Engineering, and Polymer Characterization. SML IV again marked an important step forward toward the better understanding of the kinetics and mechanism of radical polymerization, which is extremely relevant for both conventional and controlled radical polymerization and for people in academia as well as in industry.