A non-lithographic, dry approach to patterning metal nanoparticles is presented. Solutions of metal salt and polymer are spin-coated onto a substrate, dried, and exposed to a rastered microscale plasma operated at atmospheric pressure and room temperature. Interaction of the electrons in the plasma with the film results in electrochemical reduction of the metal cations to crystalline metal nanoparticles. The process is highly localized, making it possible to obtain microscale patterns of metal nanoparticles with line widths as small as similar to 30 mu m. We have applied this technique to a wide range of metals such as Ag, Au, Pt, Ir, and Ru, in various polymeric systems such as polyvinyl alcohol (PVA) and poly(methyl methacrylate) (PMMA). Overall, the approach allows the fabrication of transparent, flexible, patterned films of metal nanoparticles at low cost and high throughput for applications ranging from plasmonics to catalysis.