This book is mostly devoted to amplification of analogue signals. It covers different technologies (bipolar, MOS, and MES), and different frequency ranges but it always deals with small signals. Analogue signals processed in electronic system may have a wide variety of origins. Among them we have the signals coming from sensors (electro-mechanical, electro-magnetic, electro-chemical, electro-acoustic, electro-optical, etc.), the signals coming from antennas being produced by another electronic system or are simply cosmic produced, and signals that are generated within the electronic systems. The common property of most of the signals is their small amplitude. In many cases it is below a micro-volt. Since at the output of the system we most frequently need a high amplitude signal the main action undertaken in the electronic system before any further processing is to amplify.