Diazonium-functionalized thin films can be directly deposited in a single-step process on a wide variety of surfaces including glass, ITO, conductive carbon ink, and gold from solutions of the coupling agent p-phenylenebis(diazonium) (PPBD). These films can be reacted in a second step with various organic and inorganic nucleophiles to obtain functionalized surfaces. When acetonitrile is used as solvent, coating takes place through direct arylation of the surface by the diazonium salt, yielding a film composed primarily of polyphenylenes. Oxide surfaces do not participate in this reaction very rapidly, but can be quickly coated by solvolysis of PPBD with water as the solvent. In the latter case, the coating appears to be a poly(hydroxyazobenzene) film produced by azo coupling of phenolic groups formed by partial hydrolysis of PPBD in solution. Coatings 50-60 nm thick can be obtained with PPBD in water, while films from acetonitrile can reach 6-8 nm in thickness. Both techniques allow for surface coverage of functional groups greater than that of a single self-assembled monolayer. The rate constant of redox reactions occurring in immobilized species is reasonably rapid, on the order of 30 s -1 . The reported surface modification techniques using PPBD solutions are easy and quick, and may find use in a variety of applications in sensor design and materials science.