Pearlman's catalyst, nominally Pd(OH)₂/C, is widely used as for hydrogenation reactions and C–C coupling reactions. Contrary to the accepted view, we show that Pearlman's catalyst as prepared and after drying consists of carbon supported (mostly) nano-particulate hydrous palladium oxide capped with a monolayer of hydroxyls hydrogen-bonded to a few layers of water: a core–shell structure of C/PdO/OH/H₂O. The conventional formulation Pd(OH)₂/C from the macroscopic point of view is ruled-out by the different spectral signatures of surface hydroxyls and stoichiometric hydroxides. We also show that a minor fraction of the palladium is present as a reduced species.