This book presents the theory of quantum effects used in metrology and results of the author’s own research in the field of quantum electronics. The book provides also quantum measurement standards used in many branches of metrology for electrical quantities, mass, length, time and frequency. This book represents the first comprehensive survey of quantum metrology problems. As a scientific survey, it propagates a new approach to metrology with more emphasis on its connection with physics. This is of importance for the constantly developing technologies and nanotechnologies in particular. Providing a presentation of practical applications of the effects used in quantum metrology for the construction of quantum standards and sensitive electronic components, the book is useful for a wide audience of physicists and metrologists in the broad sense of both terms. In 2014 a new system of units, the so called Quantum SI, is introduced. This book helps to understand and approve the new system to both technology and academic community.