The appearance of quantum interference in the microscopic world is one of the deepest mysteries at the very root of quantum mechanics. When light interacts with atoms, it can induce transitions by way of distinct but indistinguishable pathways and yield unexpected and often counter-intuitive results. Electromagnetically Induced Transparency (EIT), Coherent Population Trapping (CPT), and Lasing Without Inversion (LWI) are modern examples of phenomena where the traditional rules that govern absorption and dispersion undergo major revisions. Spectacular consequences of this new state of affairs include the ability of a light beam to propagate through a normally absorbing medium with little or no absorption, or to undergo amplification even if the active medium is not prepared in a state of population inversion. Light signals have been shown to travel with strongly subluminal group velocities of only a handful of meters per second and, even, to propagate at speed greater than the ordinary speed of light, but without violation of causality or of the established rules that control the transfer of optical information through space. During my graduate studies at Drexel University, under the supervision of the late Professor Lorenzo Narducci, I explored the physical origin of the induced transparency in two configurations of three-level atoms. I developed variety of complementary approaches for the description of these systems, some semiclassical and others fully quantum mechanical. I proved the existence of quantum interference in Electromagnetically Induced Transparency and also the surprising absence of interference in a closely related phenomenon, known as the Autler-Townes effect. Furthermore, I complemented the traditional machinery of theoretical quantum optics with techniques borrowed from quantum scattering theory, and offered what I believe is the most convincing physical evidence for the appearance, or for the absence, of quantum interference effects. Working with Dr. Narducci, a Francis K. Davis Professor, an Einstein Prize winner for Laser Optics, and a recipient of Willis E. Lamb Medal for Laser Science and Quantum Optics, was a truly unique research experience with no constraints or boundaries.