Abstract : The Energetics and Warheads Division of the U.S. Army Armament Research, Development and Engineering Center has been involved in the development of CL-20. An aqueous solubility study was performed to better understand the fate and transport of CL-20 through environmental systems. CL-2O, also known as HN 1W (2,3,6,8,10,1 2-hexanitro-2,4,6,8, 10,1 2-hexaazaisowurtzitane), is a high energy, high density material. Concerns regarding the environmental fate and transport of CL-20 are arising due to its potential introduction into soil and water matrices. Work is currently being conducted to study the fate and transport of CL-20 in soil and water matrices. Determination of solubility characteristics of CL-20 in water is a preliminary task necessary to begin other fate and transport studies. The aqueous solubility of CL-20 was measured over a broad temperature range and the data were fitted to a generalized solubility model.