The interaction of extracellular polysaccharides with solid substrates plays an important role in the adhesion of bacterial cells to a variety of natural and synthetic surfaces. We have used a combination of surface infrared spectroscopy and atomic force microscopy to investigate the fundamental chemical interactions that govern the adsorption behavior of such polysaccharides. The adsorption of xanthan gum, a model polysaccharide, is studied on silicon and silica surfaces that have been modified to present a range of both surface wettability and chemical functionality. Adsorption is monitored both in- and ex-situ, using a custom-designed cell for infrared spectroscopy at silicon/aqueous interfaces. Simultaneous studies of the adsorption characteristics of the constituent monosaccharides of xanthan provide a way to assess the importance of effects such as polymer conformation and polymer-polymer interactions in the adsorption process. For instance, while monosaccharides exhibit similar adsorption characteristics on hydrophilic, silanol-terminated silica and hydrophobic, hydrogen-terminated silicon, xanthan exhibits a marked preference for the hydrophobic surface. The importance of adsorbate-adsorbate interactions in the adsorption of both poly- and monosaccharides is explored through analysis of spectral evolution from mono- to multilayer regimes.