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This paper presents a design and operational overview of the Space Station Freedom external thermal control system. The system utilizes two-phase ammonia for its operation. The paper discusses the three-loop design architecture for the overall system and its relationship to other station equipment. It also reviews the heat acquisition, transport, and rejection attributes of each as well as the thermodynamic mechanisms associated with each process. These involve ammonia boiling at the heat exchanger and coldplate heat acquisition sites, liquid ammonia supply and two-phase return flow from these sites, and direct condensing, flow-through radiators for heat rejection. Critical sizing and performance parameters such as two-phase pressure drop (and impact on loop isothermality), maximum/minimum load variations, and transient heat load variations are discussed.