A process for producing a substrate having an adhesive surface, which process comprises: (a) contacting the substrate with a carbene precursor, which carbene precursor is a compound of the following formula (1): whose substituent groups are defined herein, provided that when R is aryl or heteroaryl, said aryl or heteroaryl may be substituted by one, two, three, four or five groups, which groups are independently selected from various groups including -LB-WB; and (b) either: (i) when WA or WB comprises an adhesive functional group, generating a carbene reactive intermediate from the carbene precursor so that it reacts with the substrate to functionalise the surface, thereby yielding said substrate having an adhesive surface; or (ii) when WA or WB comprises a group which is a precursor of an adhesive functional group, generating a carbene reactive intermediate from the carbene precursor so that it reacts with the substrate to functionalise the surface, and (c) converting said group which is a precursor into an adhesive functional group thereby yielding said substrate having an adhesive surface. The invention further relates to carbene precursor compounds for use in the process, substrates produced by the process and to processes for preparing certain precursor compounds.