Microwave imaging (MI) is a class of nondestructive and noninvasive techniques aimed at inspecting targets starting from measurements of the electromagnetic field they scatter when illuminated with an incident radiation at microwave frequencies. The aim is to extract information about some of the geometrical/physical properties (e.g., the distributions of the dielectric properties) of the targets under test, often provided to the users in the form of images. However, the underlying inverse-scattering problem poses significant theoretical, numerical, and practical aspects that make this technique quite difficult and challenging. MI has been thus considered an emerging field for a long time. Across the years, engineers and scientists in universities and many other institutions devoted significant efforts in the development of new and innovative solutions, to face the challenging problem of developing effective measurement systems and data processing algorithms. Recent developments, however, allow to consider it a promising tool in several applications, such as nondestructive testing and evaluations, subsurface prospection, security, and medical imaging. In this lecture, MI techniques and their application in different fields will be reviewed. After an introduction concerning the basic concepts of the electromagnetic inverse problem (which is the basic theory of MI methods), some of the commonly adopted approaches are discussed, together with information about the related systems. Some specific examples in different applicative fields will also be provided. Finally, recent developments and future trends will be addressed.