This is a graduate course on quantum optics, aiming to equipping students with advanced knowledge of quantum aspects of light and light-matter interactions that are necessary to conduct research and to understand literatures. The course will start with classical theory of electromagnetic fields and make a transition to quantum theory. It then discusses classical and quantum description of optical systems and introduces two basic techniques for quantum measurement of light. Second half deals with interaction between optical fields and between light and matters. It will cover nonlinear optical interactions for the generation of quantum states of light, the semiclassical and quantum theories of atom-field interaction, open quantum systems. Afterward students will learn about Casmir effect, Purcell effect, polaritons, and other advanced applications.