Venous thromboembolism (VTE) presents two clinical manifestations: deep vein thrombosis (DVT) and pulmonary embolism (PE), both of which result in serious complications, and if left untreated, it may result in the death of the affected individual. While significant research has been conducted on civilians regarding the risk assessment and management of VTE, there is a scarcity of data regarding military personnel. This chapter investigates the unique challenges faced by military personnel exposed to extreme environmental conditions and stressful situations that may predispose them to VTE. Key scenarios such as prolonged stasis in submarines, high-altitude postings, extreme temperature exposure, and the microgravity environment encountered during space missions are major highlights of the chapter. The physiological and pathophysiological processes that underlie VTE in these harsh environments are also explained, which include vascular injury, hypercoagulability, and stasis. Combat-related trauma and its role in increasing the risk of VTE are given special attention. While limited data are currently available, the chapter highlights the importance of targeted studies to address these knowledge gaps. Recent research from international space agencies and military healthcare systems can provide potential insights into the mechanisms and preventative measures for VTE. This chapter serves as a foundation for understanding the implications of extreme environments on VTE risk, aiming to improve strategies for preventive measures, clinical outcomes, and operational readiness from a military perspective.