Textbook in PDF format This book presents an in-depth review of the recent interdisciplinary studies that have shed light on the mechanisms of the creation, energy transfer, and measurement of the dressed photon. A dressed photon is a type of photon that results from the interaction between light and matter in a confined space, typically on the scale of nanometers. It has been applied to nano-fabrication technologies, energy conversion technologies, and silicon light-emitting devices. Despite its extensive applications in various fields, the dressed photon's off-shell nature has posed challenges in describing it through conventional optical scientific theories