In a system with input and output signals, feedback can be introduced as a mechanism picking up part of the output signal and comparing it with the input signal (Because of the physical nature of the information, in a broad sense, the feedback is a highly transversal notion, relevant in several fields, spanning from mechanics, electronics, automation, to artificial intelligence, and cognitive neuroscience. In his books Godel, Escher, Bach: An Eternal Golden Braid and I am a Strange Loop, Douglas Robert Hofstadter assigns to the feedback an endearing role in the artificial intelligence and cognitive neurosciences fields.). After having briefly introduced a general negative feedback system, showing that the negative feedback reduces the gain, the chapter describes the benefits you obtain as a payback, such as improved linearity, reduced parametric sensitivity, and enlarged bandwidth. The effects of the negative feedback on the input and output resistances of an electronic amplifier are also addressed. The chapter describes and compares two methods (two-port and return ratio) to analyze negative feedback amplifiers. Eventually, the chapter discusses also the concept of Common Mode Feedback Bias, and it investigates the case of a non-unilateral amplifier in the feedback loop.