The book addresses defence, weapons and power-electronics aspects of High-Power Microwave (HPM) systems. It provides a detailed technical chapter on pulsed-power and power-electronics (Marx, Blumlein, LTDs, SiC/GaN switching, prime-power and energy storage), an end-to-end subsystem engineering breakdown, and operational case studies covering counter-UAS, base and shipboard protection and notable demonstrations (THOR, CHAMP). The book also evaluates deployment trade-offs, hardening and test practices, and the attendant policy and arms-control considerations for dual-use HPM technologies. This work is intended for defence scientists, military technologists, systems engineers, policy analysts, and advanced students working in directed energy, electronic warfare, pulsed power, RF/microwave engineering, and electromagnetic effects. It will also be useful to strategic studies scholars, operational planners, and decision-makers seeking a technically grounded understanding of high-power microwave capabilities, limitations, deployment trade-offs, and governance issues. High-power microwave systems are an emerging class of directed-energy technologies that use intense electromagnetic pulses to disrupt, degrade, or damage electronics-dependent targets. The subject brings together pulsed-power engineering, RF and microwave source design, antennas, coupling physics, platform integration, testing, hardening, and operational employment. It is especially relevant to counter-UAS missions, base and shipboard protection, electromagnetic spectrum operations, and the wider study of non-kinetic effects in modern warfare. It also raises important questions of escalation control, dual-use risk, ethics, verification, and arms-control governance.