In recent years, interest in the chemistry and physics of interfaces has led to the emergence of a vigorous area of research which utilizes characterization methodologies from a variety of disciplines. Central to this emergence is the recognition that interfacial phenomena play critical roles in the fabrication and performance of a variety of technologically significant materials and surface processes. Furthering the understanding of the interactions between the substrate and the adsorbate is critical to the development of a multitude of products and applications as well as advancing, on a fundamental level, the chemical and physical understanding of these interfacial phenomena;This dissertation describes the utilization of infrared external reflection spectroscopy (IR-ERS) as a means of elucidating many of the properties of polymer films and mono- and multimolecular films at both semiconducting glassy carbon and conducting noble metal surfaces. Cellulose acetate films coated on glassy carbon exhibit a marked change in permeability as alkaline hydrolysis is allowed to proceed. Infrared external reflection spectroscopy was utilized to monitor the hydrolysis of the film as the molecular composition changed from the acetate to the cellulosic form. These results are in qualitative agreement with electrochemical data obtained with cyclic voltammetry. The electrochemical measurements indicate a change in permselectivity as the hydrolysis proceeds;Monolayer films of n-alkanethiols adsorb at Au and to form highly ordered, densely packed structures with some average chain tilt from the surface normal, imparting the substrate with the properties of a pseudo-crystalline n-alkane. The average tilt angle for these adsorbates is essentially independent of chain length. This gives rise to the appearance of an odd-even effect in the methyl modes. Further, due to the mode of attachment to the surface, the orientation of the monolayer at Au is opposite that at Ag, as evidenced by the phase of the odd-even effects at the two metals;The effects of a variety of solvents on the integrity and orientation of an n-alkanethiol monolayer were studied by IR-ERS without the necessity for modulation methodologies. This dissertation reports the first in situ infrared external reflection spectra for an n-alkanethiol monolayer at Au and Ag in the presence of a variety of solvents without the need for potential or polarization modulation. Descriptions provided by such measurements promise to expand the understanding of the fundamental intermolecular forces that control the chemical and physical properties of these interfaces. Further, this technique has far-reaching applicability to a variety of other interfacial systems with varying properties.