In the previous chapter the syntheses of thiols and disulfides were described. In this chapter experiments aimed at the characterization of monolayers of these compounds on gold will be presented. Characterization of a layer involves determination of the surface elemental composition, for example by XPS, which is important in that it helps establish that the desired compound is adsorbed. As will be seen, this is also valuable in determining the nature and source of contaminants which may adsorb during sample preparation. Other techniques such as electrochemistry and contact angle measurements indirectly probe the monolayer structure, whereas scanning probe microscopy (STM and AFM) allows a more direct visualization of the nature of the surface.