This book is written for students who ever wondered about the mysterious and fascinating world of particle accelerators. What exciting physics and technologies lie within? What clever and ingenious ideas were applied in their seven decades of evolution? What promises still lay ahead in the future? Accelerators have been driving research and industrial advances for decades. This textbook illustrates the physical principles behind these incredible machines, often with intuitive pictures and simple mathematical models. Pure formalisms are avoided as much as possible. It is hoped that the readers would enjoy the fascinating physics behind these state-of-the-art devices. The style is informal and aimed for a graduate level without prerequisite of prior knowledge in accelerators. To serve as a textbook, references are listed only on the more established original literature and review articles instead of the constantly changing research frontiers.