The primary focus of this thesis is the study of bimetallic ordered surface alloys. Cu-based bimetallic catalysts show very useful properties, particularly in respect to their industrial applications, such as metal selectivity, structural stability and catalytic activity in comparison to their single-metal counterparts. Since most microelectronic assemblies utilize Pb-Sn solders for interconnection and modern environmental regulations have targeted the elimination of Pb usage, this makes research for “Pb-free” solders an important issue for microelectronics assembly. Thus the Cu-Sn bimetallic system is a technologically important system which merits detailed investigation. The Sn/Cu(100) surface system has five reported submonolayer surface phases. Four phases were originally reported by Argile and Rhead in the early 1980’s and a fifth phase was reported by Martinez-Blanco et al. in 2006. This thesis has been motivated by this report of a new surface phase. The original four phases have already been studied using Low Energy Electron Diffraction (LEED) by McLoughlin et al. This thesis reviews these studies and completes them by analysing LEED images and integral order beam I(V) spectra obtained for the most recently reported phase. The surface structures of all five phases are studied using Scanning Tunnelling Microscopy (STM) and surface structure models for all the phases are proposed. Photoemission Spectroscopy (PES) and High-Resolution Core-Level Spectroscopy (HRCLS) studies were carried out using synchrotron radiation in the Institute for Storage Ring Facilities in Aarhus (ISA). PES is used to measure changes in the work functions and valence band spectra while HRCLS is used to examine differences in the Cu 3p and Sn 4d core level spectra for all five phases.