Active Galactic Nuclei (AGN) are the most luminous persistent sources in the Universe, and are believed to be powered by accretion onto supermassive black holes. My work is mainly focused on the study of X-ray spectra of AGN, with particular attention to the unification scenarios. AGN are classified according to their optical spectra, and different types of AGN are thought to be intrinsically the same object, just observed from different lines of sight with respect to a molecular torus. In this work, differences between different classes of AGN, unforeseen by the unification model, are found. These differences appear to be due to a larger reflection component in the spectra of more obscured objects, which could be related to the latter having on average more material around than the former.