Magnetism is highly sensitive to the local atomic environment, a property that is at the origin of the unique magnetic behavior induced by the large ratio of surface or interface atoms to bulk atoms in nanostructures and ultrathin films. One key property of strong relevance in technology is interface-induced perpendicular magnetization anisotropy, which often is observed in ultrathin magnetic layers of only a few atomic planes. Establishing the existence of this phenomenon required an improved control of the growth modes, and advances in its understanding required detailed structural studies coupled with sensitive magnetic characterization. While magnetic nanostructures have been mainly realized using molecular beam epitaxy, the preparation of magnetic nanostructures in the electrolytic environment has become possible, with a degree of control that is comparable to that achieved in ultrahigh vacuum. This article reviews recent studies about epitaxial ultrathin magnetic layers electrodeposited on Au(111) single crystal electrodes with emphasis on in situ structural and magnetic characterization. This article also demonstrates that surface magnetism is very sensitive to the electrochemical interface.