This book is written for the learner's point of view, with the purpose of helping readers understand the principles of flow. The theory is explained using ordinary and accessible language, where fluid mechanics is presented in analogy to solid mechanics to emphasize that they are all the application of Newtonian mechanics and thermodynamics. All the informative and helpful illustrations are drawn by the author, uniting the science and the art with figures that complement the text and provide clear understanding. Another unique feature is that one of the chapters is wholly dedicated to providing 25 selected interesting and controversial flow examples, with the purpose of linking theory with practice. The book will be useful to both beginners in the field and experts in other fields, and is ideal for college students, graduate students, engineers, and technicians.