The electrochemical treatment of Pd electrodes in acid solutions by means of periodic potentials applied within certain potential windows in the range 0–1.5 V (vs. RHE) and frequencies in the range 0.5–6.25 kHz, produces surface modifications involving different types of roughening and faceting. These modifications are the consequences of various electrochemical reactions occurring during the oxidation-reduction cycles, mainly associated with the electrodissolution-electrodeposition of Pd, and oxide layer formation-electroreduction processes. Quantitative data are shown about the former con- jugated processes which indicate that, depending on the frequency range, at least three different mechanisms operate for the entire reaction. Surface modifications are followed through voltammetry, scanning electron microscopy and scanning tunneling microscopy.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas