Recent experimental studies of the structure of surface alloy phases and of the surface of bulk alloys have revealed the existence of interfacial stacking faults in Sb on Cu(I 1 1) and Ag(l 1 1), the reduction in effective atomic radii manifested by reduced rumpling amplitudes in surface alloys, and evidence for local disorder at the surface Of Pt25Rh75(l 1 1). A brief review of some of these phenomena and their associated systematics is presented, together with the results of new density functional theory (DFT) calculations aimed at gaining insight into the issue of surface alloy rumpling and effective atomic radii in such surface phases. In particular, by comparing interatomic distances in bulk and surface alloys we show the reduced rumpling in surface alloys is a true surface effect, independent of the definition of atomic radius. (C) 2003 Elsevier Science B.V. All rights reserved.