Surface modifications by polymers are becoming increasingly important for various applications ranging from biotechnology to advanced microelectronics. Recent successful applications of living radical polymerization (LRP) made it possible to graft various low-polydispersity polymers including simple homopolymers, end-functionalized polymers, block/random/gradient copolymers, and functional polymers. At the same time, this technique has brought about a striking increase of graft density. Graft chains in such a high-density polymer brush were found to be highly extended in good solvent, even to the order of their full lengths. It was also found that a high-density polymer brush has characteristic properties, in both swollen and dry states, quite different and unpredictable from those of the semi-dilute or moderately dense polymer brushes previously studied. This review highlights the recent development of surface-initiated LRP and the structures, properties, and potential applications of thereby obtainable high-density polymer brushes. It is believed that surface-initiated LRP is opening up a new route to "precision" surface modification.