Harnessing Light is a text on Photonics, aimed to undergraduate and recent postgraduate engineers and physicists interested in this fascinating topic. In Photonics, light is tamed and manipulated to deploy its powerful properties in a myriad of applications. The approach adopted in this text is intended to ease the way into the main concepts. The goal of each Section is finding the best way to describe the involved phenomena, alleviating mathematical formulations that sometimes hinder the core of the topic. When required, mathematical supports are shown in separate Appendices. The Sections are divided into three parts, namely, an introduction of the fundamental background required for the concepts at hand, a detailed study of light generation, transmission, and detection, preferentially dealing with semiconductor sources and detectors since they are involved in many common photonic areas. The third part includes detailed descriptions of some specific photonic devices of the highest relevance: the eye, digital cameras, and displays.