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 is described, along with NOON states and their application in super-sensitivity, super-resolution and quantum lithography. Applications of entanglement and coincidence measurements are described including ghost imaging, quantum illumination, absolute photodetector calibration, and interaction-free measurement. With quantum optics playing a central role in the so-called “second quantum revolution,” this book, equipped with plenty of exercises and worked examples, will leave students well prepared to enter graduate study or industry.