This book provides the reader with a detailed theoretical treatment of the key mechanisms of superconductivity, up to the current state of the art (phonons, magnons, plasmons). In addition, the book describes the properties of key superconducting compounds that are of most interest for science and its applications today. For many years there has been a search for new materials with higher values of the main parameters, such as the critical temperature and the critical current. At present, the possibility to observe superconductivity at room temperature has become perfectly realistic. The book is especially concerned with high Tc systems, such as the high Tc oxides, hydrides with record values of the critical temperature under high pressure, nanoclusters, etc. A number of interesting novel superconducting systems have been discovered recently. Among them: topological materials, interface systems, intercalated graphene. The book contains rigorous derivations, based on statistical mechanics and many-body theory. The book is also providing qualitative explanations of the main concepts and results, which makes it accessible and interesting for a broader readership.