The primary focus of this PhD is the investigation of pentacene thin films grown on metal substrates. Numerous techniques have been used to investigate these films including synchrotron based photoelectron emission spectroscopy (PES) and near edge x-ray absorption fine structure (NEXAFS) techniques in addition to scanning tunnelling microscopy (STM) and low energy electron diffraction (LEED) techniques. The two primary experimental systems that have been studied are the pentacene/Au(100) and the pentacene/Cu(l 10) systems. In both pentacene/metal systems the molecules were found to bond flat, or nearly flat to the substrate, with a significantly stronger bond observed between the pentacene and Cu(l 10) substrate. In addition to these studies, secondary studies involving the manipulation of the properties of pentacene films have been investigated. This investigation has been carried out through the use of interlayers and film doping. Interfacial layers of sulphur and oxygen were deposited on the Au(100) and Cu(110) substrates respectively prior to the deposition of pentacene in order to investigate changes in the interfacial interaction of the pentacene and underlying substrate. These studies were carried out using PES. Additional PES experiments were carried out to investigate the alkali metal doping of the pentacene/Cu(l 10) system using sodium in order to alter the injection characteristics of the organic/metal system. The effects of different levels of ordering in the molecular film were found to influence the doping of the molecular film.