For the growing need in wireless spectrum by wide bandwidth applications such as ultra-high data rate transfer, at speeds of 10 Gbps and up, millimeter wave plays important role in providing reliable spectrum solutions. Worldwide R&D in millimeter wave area has demonstrated many successful tests to establish the technology with its promising potential for the future of defence and security. This monograph explores the design and implementation of millimeter wave active/passive circuits and systems using waveguide/MMIC (Monolithic Microwave Integrated Circuit) and planar waveguide technology. Extensive use is made of photographs of systems, line diagrams showing various techniques, and important system characteristics. It begins with an introduction to frequency bands, unique millimeter wave applications in communication. It presents detailed discussions about millimeter wave devices and circuits, generating devices, e.g., IMPATT oscillators and Gunn oscillators, where concept of injection locking phenomenon in oscillators and power combining techniques, etc., have been highlighted. Receiver components, millimeter wave transceiver configurations and development of millimeter wave systems technology useful for defence services are presented. It also discusses future trends and technology challenges which enlighten about exploitation and challenges of millimeter wave frequency spectrum in futuristic military applications such as broadband communication technology, optical technique of millimeter wave generation with low phase noise signal for applications in imaging and phased array radar systems and millimeter wave options for mobile cell phones. The book is written to support and supplement millimeter wave and subsystems/system courses of scientific institutions/university as well as a reference for researchers, professionals, and high RF frequency design engineers working in this exciting field of millimeter wave technology.