Surface modification through reduction of aryldiazonium salts to give covalently attached layers is a widely investigated procedure. However, realization of potential applications of the layers requires development of patterning methods. Here, we demonstrate that microcontact printing with poly(dimethylsiloxane) stamps inked with aqueous acid solutions of aryldiazonium salts gives stable organic layers on gold, copper, silicon, and graphitic carbon surfaces. Depending on the substrate-diazonium salt combination, the layers range from relatively irregular multilayers to smooth films with close to monolayer thickness. After printing, surface attached aminophenyl and carboxyphenyl groups retain their usual reactivity toward amide bond formation with solution species, and hence, the method is a simple route to patterned, covalently attached, reactive tether layers. Multicomponent patterned films can be prepared by printing a second modifier onto a film-coated surface. Microcontact printing using aryldiazonium salt inks is experimentally very simple and is applicable to the broad range of substrates capable of spontaneously reducing aryldiazonium salts.