While many articles have been written on microwave devices, a great majority of them are prepared for specialists dealing in specific aspects of microwave engineering. At the same time, material at a fundamental level in tutorial form is extremely limited, especially for stu dents who need to acquire basic knowledge in the field. Individuals seeking to gain a prelim inary understanding of microwave circuits are usually relegated with little success to the end less search from one reference source to another. For non-experts, sequential derivations of basic relations are rarely available and extremely difficult to locate. The purpose of this volume is to collect in one place the essential fundamental principles for a group of microwave devices. The chosen devices are those which form the basic modules found in practical microwave systems. Thus, these devices provide the crucial build ing blocks in common microwave systems, and their inherent characteristics are also the basis of some of the fundamental concepts in more complex devices. The material is presented in a continuous, self-contained manner. With the appropriate background, readers should be able to follow and understand the contents without the need for additional references.