The electrochemical behavior of small metal nanoparticles is governed by Coulomb-like charging and equally spaced charge-transfer transitions. Using electrochemical gating at constant bias voltage, we show, for the first time, that individual nanoparticles can be operated as multistate switches in condensed media at room temperature, displaying distinct peak features in the tunneling current. The tunneling conductance increases with particle charge, suggesting that solvent reorganization and dielectric saturation become increasingly important. © 2007 American Chemical Society.