The synthesis of hybrid nanoparticles was conducted by the atom transfer radical polymerization (ATRP) of styrene and (meth)acrylates from colloidal surfaces. Colloidal initiators were prepared by the functionalization of silica colloids with 2-bromoisobutyrate groups. ATRP from colloidal surfaces was then performed to attach well-defined homopolymers and block copolymers to an inorganic core. Kinetics of the ATRP of styrene (Sty), n-butyl acrylate (BA), and methyl methacrylate (MMA) under identical reaction conditions were investigated. Hybrid nanoparticles containing block copolymers of pSty-b-pBA (M-n = 22 300; M-w/M-n = 1.20), pMMA-b-pBA (M-n = 29 400; M-w/M-n = 1.28), and pBA-b-pMNIA (M-n = 17 300; M-w/M-n = 1.28) were prepared, and hydrolysis of silica cores by hydrofluoric acid treatment enabled characterization of cleaved copolymers using size exclusion chromatography and H-1 NMR. Ultrathin films of hybrid nanoparticles were examined using transmission electron microscopy and atomic force microscopy.