We describe the in situ synthesis of nanometer thick films of polystyrene (PS) on a self-assembled monolayer (SAM) on gold by surface-initiated free radical polymerization and further demonstrate that three-dimensional polymer structures with micrometer lateral resolution and nanometer vertical resolution can be fabricated by combining microcontact printing (μCP) with surface-initiated polymerization (SIP). We implemented SIP onto a COOH-terminated SAM on gold using a sequential approach to couple an amine-terminated free radical initiator to the terminal COOH groups presented by the SAM, followed by free radical polymerization of styrene. Each step of SIP was characterized by X-ray photoelectron spectroscopy and ellipsometry, and the PS film and micropattern were also characterized by atomic force microscopy. We typically obtained PS films with a thickness of 10−20 nm for a polymerization time of 12−24 h and with a root-mean-square roughness of ≤0.5 nm. PS micropatterns were also successfully fabricated ...