This publication describes the three computer models Federal agencies and the Northwest Power Pool use regularly to help plan hydro operations in the Columbia River Basin: HYSSR, HYDROSIM, and HYDREG. It is one of a series of booklets written for participants in the System Operation Review (SOR) being conducted jointly by the US Army Corps of Engineers (Corps), the US Bureau of Reclamation (Reclamation), and theBonneville Power Administration (BPA). A list of the other publications appears on the inside front cover. The SOR is the environmental analysis required to consider changes in Columbia River system operations related contract arrangements. Over the next few years, the agencies will develop a new multiple-use operation for the Columbia River. At the time, the Pacific Northwest Coordination Agreement (PNCA) and other contracts related to the Columbia River Treaty between the United States and Canada will be renegotiated and renewed. Many alternative ways of operating individual projects and the river system as a whole will be considered in the SOR. To analyze how these changes would affect the system's ability to meet its multiple-use goals, various operating scenarios will be thoroughly evaluated. The three computer models, HYSSR, HYDROSIM, and HYDREG, will play an important role in this evaluation.