The field of microfluidics has become one of the most dynamic disciplines of microtechnology. On the one hand, microfluidics offers the mere benefits of miniaturization, enabling many fields of application, in particular where small liquid volumes, transportable and cheap devices, or integrated process control are beneficial. On the other hand, microfluidics provides an elegant and often exclusive access to the nanoworld of biomolecular chemistry and cell handling, leveraging many novel biotechnological applications. This chapter first outlines the fluidic properties and working principles underlying microfluidic devices, such as diffusion, heat transport, interfacial surface tension, and electrokinetic effects. It then introduces fabrication techniques and sketches microfluidic components for flow control, pumping, physical sensing, and dispensing and their applications in (bio-)analytical chemistry, drug discovery, and chemical process engineering.Microfluidic devices are one of the earliest success stories in the commercialization of microelectromechanical systems (MEMS). Efforts to dispense minute amounts of liquid at high precision date back to the early 1950s and constitute the basics of contemporary inkjet technology. Since then, enterprises have continuously improved and diversified this technology, the worldwide annual revenues of which currently approach $10 billion.With the groundbreaking progress in microtechnology, starting in the 1970s, other types of microdevices were developed in academic and industrial labs. "Killer" applications such as microelectronic memory chips and processors as well as microelectromechanical read/write heads for hard disks shine, with staggering growth rates in performance and revenues. When MEMS were still chiefly an academic topic in the 1980s, microfluidic research focused on miniaturized conventional components. The first microfabricated pumps and valves were presented; they relied basically on the same principles as their macroscopic counterparts.