This is a free, online wikibook, so it is continually being updated and revised. According to the authors, "This novel electronics wikibook is for you - creative thinking students, teachers, inventors, technicians, hobbyists and for all those who do not feel happy with formal circuit explanations. It is intended for people who want really to grasp the basic concepts of electronics relying rather on their human imagination, intuition and emotions than on logical reasoning. Revealing the mystery of negative impedance.This book is part of a series on Electric Circuits: Circuit Theory, Circuit Idea, Digital Circuits, Practical Electronics, Electronics, Analogue Electronics, Semiconductors, and Materials in Electronics. Electronic circuitry is more art than science. Inventing novel electronic circuits is a result of human fantasy, imagination and enthusiasm. Fortunately, abstract electronic circuits are based on clear and simple ideas, which we may derive from our human routine. In order to really understand how circuits operate, we have first to reveal the basic ideas on which they are grounded. We just need to know what problem the electronic elements solve, why they are connected there, what they actually do in the circuit, how they do what they do, etc. As human beings, we just want "to see the forest for the trees". Great circuit ideas are "non-electrical"; they do not depend on the specific implementation (tube, transistor, op-amp etc.), they are eternal. The purpose of this wikibook is to reveal great circuit ideas, real truth about circuits. It just answers a simple but reasonable question: What is the idea behind the circuit?