This chapter discusses the developments and the use of electronic negative feedback amplifier. The comparison in the developments in telephone and then wireless communication systems illustrates the great significance of Black's recognition that negative feedback has benefits other than simply providing stability. In examining the way in which 'feedback' has been used in radio applications, Black clarified understanding and through his realisation that the behaviour of the complete system could be modified by changing the passive components in the feedback network, he pointed the way forward. John Taplin of MIT adapted the Nyquist tools for use in general feedback systems in about 1937 when he applied the techniques to a servomechanism. The use of frequency response techniques for investigating system performance led to attempts to relate frequency and transient response data. For the dominant position occupied by frequency domain techniques for control system design. The search of the communication engineers for methods of achieving stable frequency oscillators epitomises the use of negative feedback.