This volume from the successful Macromolecular Symposia series presents the contributions from the IUPAC-sponsored International Symposium on "Radical Polymerization: Kinetics and Mechanism", held in Il Ciocco, Italy, in September, 2006. This 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 controlled radical polymerization. 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. Here, top international authors, such as K. Matyjaszewski, T. P. Davis and T. Fukuda, 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.