Signal amplifier is an electronic device that amplifies the signal applied at the input and delivers an amplified signal at the output. When a part of the output signal is taken and mixed with the input signal, the process is called feedback. Feedback may be of two types; positive feedback in which the feedback part of the signal is in-phase with the input signal, and therefore, the overall gain of the amplifier increases. However, if the feedback signal is out of phase, the overall gain decreases and the process is termed as negative feedback. Both positive and negative feedbacks are frequently used; former to convert an amplifier into Oscillator and later to stabilize the amplifier operation. Details of the two types of feedbacks, methods of achieving them, their effect on the performance of two port networks, etc. are discussed in this chapter.