Studies on the interfacial properties of palladium electrodes have yielded phenomena that help to establish the rich chemistry that occurs at the surface of this metal.  Such unique phenomena are showcased in this review.  The discussion is centered around the following interrelated subjects: (i) electrode-surface coordination chemistry, (ii) adsorbate-activated electron-transfer sites, and (iii) adsorbate-induced substrate reactions.  The experimental procedures adopted in these studies relied upon a combination of electrochemistry, in situ scanning tunneling microscopy, and ultrahigh vacuum surface spectroscopy.