Quantum Key Distribution (QKD) is a technology that ensures secure communication by leveraging the principles of quantum mechanics, such as the no-cloning theorem and quantum uncertainty. This chapter provides an overview of this quantum technology's maturity and trends. It highlights significant advancements in single-photon sources and detection technologies that have brought QKD closer to widespread adoption, including real-world deployments by industry leaders. While addressing challenges such as cost, integration, standardization, and the need for quantum repeaters, the chapter emphasizes the growing importance of QKD in securing mission-critical communications against future quantum threats. Through its unique ability to achieve information-theoretic security, QKD is poised to play a vital role in quantum-safe cryptographic algorithms and protocols.