This book analyzes the development of space light-fiber coupling research, highlights its importance, examines the underlying theory and key problems, and elaborates on methods to improve the space light-fiber coupling efficiency. Starting from the basic theory of electromagnetic field, the transmission characteristics of light in optical fibers are expounded, and the coupling characteristics of optical signals of different modes are investigated. The spatial light-fiber coupling techniques such as mode conversion method, lens coupling method, and wavefront distortion correction method are discussed in detail, and the key technologies involved are verified by experiments. This book is suitable for the vast majority of engineering and technical personnel and teachers in colleges and institutions who are engaged in wireless optical communication. It can also be used to train senior undergraduates and graduate students in relevant fields.