Quantum Key Distribution (QKD) is a revolutionary security technology that exploits the laws of quantum mechanics to achieve information-theoretic secure key exchange. QKD enables two parties to “grow” a shared secret key without placing any limits on an adversary’s computational power. QKD is unique because it exploits the fundamental laws of quantum mechanics to detect the presence of any third-party eavesdropping on the key exchange. In this chapter, we present a historical survey of the development of QKD systems and their system architectures, identify commercially available QKD system solutions, discuss emerging trends in the research of future QKD technologies, and present a use case that demonstrates the utility of QKD technology in a real-world military scenario.