Radar and communication systems play an important role in civil and military applications. They are always under development and new versions continually come to the market. Though the basic operation principles have stayed nearly the same over the last 100 years, new technology has allowed for advancements in the development of components, and new systems find specific applications. Superconducting materials are widely used, for example in motors, magnets, cavities, and transformers, and are sometimes also used for typical components of radar and communication systems, like antennas, filters, and logical elements. Superconducting components significantly change the operation of whole systems, and thorough understanding of operational principles is of paramount importance for correct design. In this book, the recent developments of cryogenic receivers over the last 20 years are outlined. Special attention is given to the very specialised technologies, like Rapid Single Flux Quantum (RSFQ) logics, or electrically small active antennas based on SQUID/bi-SQUID/SQIF operational principles. The classical applications, like superconducting filters or cryogenically cooled Low Noise Amplifiers (LNA), are considered in detail. Though the book is considered as a review on recent developments of cryogenic receivers to facilitate an understanding of operational principles, many examples with estimations are given. The reliability of cryogenic receivers strongly depends on the mechanical and cryogenic designs, and many practical examples and solutions are also presented. Future trends or possible research areas are considered as well. This book will be helpful for graduate students as well as engineers working with cryogenic, radar and communication systems.