This chapter provides the basics for understanding visual servoing. X‐ray imagers. It focuses on the conventional visual sensors such as charge coupled device (CCD) or complementary metal oxide semiconductor (CMOS) cameras, and also on imaging devices typically encountered in the medical field. The chapter reviews these systems in terms of a “real‐time” usage. Indeed, the realization of a visual servo loop requires precise modeling of the chronology of events from the acquisition of the image to the sending of control signals to the robot. The chapter also addresses the issue of the robust extraction of visual information in the particularly difficult context of in vivo images. Several types of control laws are applicable to a visual servoing. The chapter discusses their appropriateness depending on the application.