One author participated in the research of the invention of early fiber lasers and the other is still exploring the forefront of this field, aim to introduce fiber lasers to readers from three aspects: principles, technology, and applications. Graduate students and doctoral candidates in higher education institutions can learn the principles of fiber lasers from this book, and perhaps also learn how to find research directions. Readers engaged in technological development work in startups in the optoelectronics field can learn about the technology, and perhaps also gain inspiration for innovation from the chapters describing experimental design and technology introduction. Engineers designing applied products can understand the recent developments and future prospects of fiber lasers, and perhaps also be inspired to design new products from the continuously expanding history of fiber laser applications.