Reservoir regulation by Columbia Treaty Projects, in conjunction with existing U.S. Columbia Treaty Projects, will provide assured control of major floods to reasonably safe levels. A flood control operating plan for the Treaty Projects has been developed in accordance with Treaty requirements. This paper describes the flood characteristics of the Columbia River, the principles of flood regulation, and the methods used in developing the flood control operating plan. A summary of results of flood regulation studies for the 30-yr. period, 1929–1958, together with the flood of 1894, the maximum flood of historic record, are presented.