Radars in the millimeter wave range are used today in a variety of different applications that were unthinkable ten or more years ago. Radar circuits are now available highly integrated in silicon, very robust and mass-produced assembly and interconnect technologies are available and frequency regulation allows many new applications, especially in the ISM bands. The main fields of application are briefly presented in this chapter. However, as development in the field of radar sensor technology is currently progressing very rapidly, it is hardly possible to provide a complete overview of all applications.