Porphyrins adsorbed on surfaces may undergo several reactions with the surface, including metalation, where a metal atom from the surface is inserted into the porphyrins molecule, and dehydrogenation, fusing adjacent molecules or pyrrole and phenyl rings within one molecule. Using synchrotron- and laboratory-based XPS, NEXAFS and TPD measurements, examples will be given of reactions of tetraphenylporphyrin molecules with oxide and metal surfaces, both in ultrahigh vacuum and in aqueous solution.