This book discusses the fundamentals of electromagnetic waves and applications of their properties. It describes transmission line theory and principles of microwave junction used for power division, addition and measurement systems. The book presents the full spectrum of both passive and active microwave components, and deals with various types of tees, directional-couplers, isolators, circulators, gyrators along with scattering parameters required for the analysis of microwave circuits, and describes microwave sources, e.g. klystrons, magnetrons, etc. and semiconductor devices. Besides, it explains the laboratory procedures for measurements of various parameters of circuits working at microwave frequencies. This textbook is suitable for the undergraduate and postgraduate students of Electronics and Communication Engineering.