This first volume of the series Lectures in Optics introduces the simplest optical phenomena and the simplest optical instruments. Among these phenomena, rectilinear propagation, reflection, and refraction dominate the optical effects in nature and are essential to understanding the function of simple optical devices. Introduction to Optics presents the arguments relating to the nature of light and its propagation, the basic interactions between light and matter, and the energy aspect of light in relation to the quantitative measurement of visible radiation (photometry). It covers the fundamental laws governing reflection and refraction, as well as their applications in prisms and atmospheric phenomena. Simple optical instruments such as the pinhole camera, the human eye, the microscope, the telescope, and the photographic camera are covered. The text is accompanied by copious diagrams and striking photographs whose visual appeal entices readers to delve into the concepts. This book is suitable for various levels of instruction, from high school upper-level STEM classes to entry-level college optics 101 courses. Practice examples throughout the chapters reinforce an understanding of the presented material.