Microfluidics deals with fluids flowing in miniaturized systems. It is a young discipline, which is expected to substantially expand over the next few years, stimulated by the considerable development of applications in the pharmaceutical, biomedical and chemical engineering domains. The book is an introduction to this discipline. In the first chapter, it presents a short historical background and discusses the main perspectives of the domain, at economical and scientific levels. Then the physics of miniaturization and the fluid mechanics of microflows are discussed. In the following three chapters, dispersion, electrical and thermal phenomena in miniaturized devices are presented. A brief introduction to microfabrication techniques is given in chapter six and the book concludes by providing a few examples of microfluidic systems. The book is written in a simple, direct, pedagogical way. It emphasizes concepts and understanding, rather than technical detail. It offers a cross-disciplinary view of the field embracing biological, chemical, physical and engineering perspectives. By using the book, the reader will have concepts, methods and data to grasp situations which typically arise in microfluidic systems.