The structure of electrodeposited iodine-from a potassium iodide (KI) electrolyte-at the Au(111) surface has been investigated using surface X-ray scattering (SXS) techniques. Two distinct incommensurate iodine monolayer phases are observed. In both of these phases the structures compress with increasing potential (electrocompression). In the lower potential phase a (pX root 3) centered-rectangular iodine monolayer is observed in which the coverage (theta) increases from 36.6% to 40.9% (relative to the gold layer density) with increasing potential. At more positive potentials a rotated-hexagonal phase is formed, and theta increases from 41.5% to 44.5%. At the highest coverages, in both phases, the iodine-iodine nearest-neighbor spacing equals the van der Waals diameter of 4.3 Angstrom. Analysis of the specular reflectivity gives an iodine-gold interlayer spacing of 2.35 Angstrom and iodine coverages which are in good agreement with the in-plane diffraction results.