Soft interfaces formed by polymer materials are important interfaces for biological systems (biointerfaces). Controlled radical polymerization (CRP) is highly suited for designing biointerfaces composed of polymer chains because it enables precise control of the polymer architecture at the nanoscale. This focus review describes the design of functional soft interfaces based on investigations of the structure-property relationships of CRPs. In particular, polymer brush surfaces showing autonomous property changes, comb-type copolymer-driven 2D/3D transformations of lipid bilayers, and molecular interactions in bactericidal cationic polymer brushes are depicted.