An adhesive is prepared by condensing a phenol, preferably a polyhydric phenol, and furfural to form a fusible soluble partial condensate, dissolving the same in a volatile organic solvent, further condensing it in the presence of an acidic condensation catalyst to a point short of that to which the condensate becomes infusible, and adding to the solution thus obtained a solution in a volatile organic solvent of a vulcanizable natural or synthetic rubber. Preferably the partial condensate is prepared by heating substantially equal proportions of a phenol and furfural to a temperature of about 80 to 110 DEG C. for about 1 to 6 hours. Alternatively an excess of one reagent may be employed or an alkaline condensation catalyst may be present. The further condensation is preferably carried out below about 40 DEG C. and the reaction mixture may be cooled. The solvent for the partial condensate may also be a solvent for the rubbery material, but the solvent for the rubbery material is preferably not a solvent for the phenol-furfural condensate. The two solvents should, however, be miscible. The adhesive may also comprise pigments, fillers, softeners, vulcanizing agents, vulcanization accelerators, and condensation and polymerization inhibitors, for example aliphatic mercaptans and phenylhydrazine. The adhesive may be used for securing natural or synthetic rubbers to metal, plastics, concrete and wood. Materials specified are: phenols: phenol, cresols, xylenol, resorcinol, naphthol, pyrogallol, phloroglucinol, hydroquinone; solvents for the partial condensates: ketones, e.g. methyl ethyl ketone or cyclohexanone; esters, e.g. butyl butyl acetate, butyl propionate, and cyclohexyl acetate ethylene dichloride; catalyst: amine hydrochlorides, e.g. hydroxylamine hydrochloride, a mineral acid or a metal chloride; natural rubber, e.g. heven or guayule; synthetic rubbers; polymers of aliphatic open-chain conjugated diemes, e.g. butadiene, di-methyl butadiene, piperylene, isoprene, methyl pentadiene, chloroprene or their copolymers with each other or with polymerisable compounds containing a single olefinic double bond, e.g. acrylonitrile, acrylic and substituted acrylic ester such as methyl acrylate and methyl methacrylate, styrene and its substitution products, vinyl ketones, vinylidene chloride, isobutylene. In an example equal parts by weight of resorcinol and furfural are heated in the range 85 to 110 DEG C. for about 4 hours, cooled to below 80 DEG C. and dissolved in methyl ethyl ketone. The solution is further condensed at 30 DEG C. in the presence of hydroxylamine hydrochloride and there is added a solution in ethylene dichloride of the copolymer of butadiene and acrylonitrile.