Superconductors are quantum materials, where some electrons coallign themselves to produce their weird properties, notably the zero electrical resistivity at low temperature. Although superconductors were discovered long time ago, (in 1911) and thousands of researchers (among them 15 scientists were awarded Nobel prizes in this field) have dedicated their scientific efforts to uncover this phenomenon, the true cause of superconductivity is still a challenging puzzle till now. Actually there exist some elegant theories to explain the superconductivity phenomenon, such as, the BCS theory (Bardeen, Cooper & Schrieffer, 1956). Unfortunately, these theories are only applicable to a special class called conventional superconductors. Actually, these theories were originally dedicated to explain low-temperature superconductors (LTS), whose critical temperatures are less than 30K (-243 C). After the discovery of high-temperature superconductors in 1987 (with T>30K), it has been established that the BCS is not adequate to describe this class of super-conductors, which have been called unconventional superconductors. Indeed, it is strongly believed that there exist a common cause of super-conductivity in all superconductors, but this cause remains a challenge in condensed matter science since the last century. In fact, the common mediating mechanism by which the electrons are attracted (in pairs, in spite of their natural repulsion) in all superconductors is still an enigma. The main purpose of this book is to develop a deep understanding of the true cause of superconductivity, with a new theory, which is applicable for all types of superconductors. I mean by the word “all” both conventional and unconventional superconductors, which scientists believe to have all the same origin of superconductivity. This understanding will certainly lead to the development of the long-time-dreamed room-temperature superconductors (RTS). Needless to say, the advent of stable RTS materials will make a revolutionary change in the electric power, electronics and computer industries.