The underpotential deposition (upd) and bulk deposition of Ag on Au(111) has been investigated in H 2 SO 4 and HClO 4 solutions using electrochemical scanning tunneling microscopy (STM). Theupd of Ag occurs in three steps on Au(111) in both solutions. A (3 3)R30° structure was found for the first adlayer of Ag in pure H 2 SO 4 solution. In HClO 4 solution, a (4 4) structure was found in the potential range between 0.85 V and 1.10 V vs. rhe. A (1 1) structure appeared after the formation of the third upd adlayer, indicating that a close-packed Ag layer was epitaxially formed in the third upd process. Bulk deposited Ag films showed a rolling hill structure in the beginning but became smoother with time due to surface diffusion. An Ag(111)-(1 1) structure was observed for the bulk deposited Ag surface.