The surface-induced polymerization of a chromophore-functionalized monomer was probed in situ for the first time using a nonlinear optical technique, second-harmonic generation. During the first hours of the polymerization reaction, dramatic changes in the tilt angle of the chromophore-functionalized side groups were observed. Following evaluation of the nonlinear optical data with those obtained from atomic force microscopy and ultraviolet-visible, we conclude that second-harmonic generation efficiently probes the polymerization reaction and the conformational changes of the surface-grafted polymer. With polymerization time, the conformation of the surface-tethered polymer changes from a conformation with the polymer backbone and its side groups flat on the surface, i.e., a “pancake” conformation, to a conformation where the polymer backbone is stretched away combined with tilted side groups or an enlarged tilt angle distribution, i.e., a “brush-type” conformation.@en