This book, based on classroom-tested lecture notes, provides a self-contained one semester undergraduate course on quantum optics, accessible to students (and other readers) who have completed an introductory quantum mechanics course and are familiar with Dirac notation and the concept of entanglement. The book covers canonical quantization, the harmonic oscillator, vacuum fluctuations, Fock states, the single photon state, quantum optical treatment of the beam splitter and the interferometer, multimode quantized light, and coherent and incoherent states. Metrology is a particular area of emphasis, with the book culminating in a treatment of squeezed light and its use in the laser interferometer gravitational-wave observatory (LIGO). The Heisenberg limit