The major impacts of systems techniques on the planning process in the North Atlantic regional water resources study are described. The techniques discussed are an input-output-based demand projection model and a mathematical programing supply model. The impacts discussed relate to the coordination and control of the planning process, the consideration of multiple objectives, the assessment of uncertainty, the efficiency of planning, the scope for the exercise of judgment, and the opportunity for a planning process continued beyond the final report. The writer concludes that the impact of systems techniques has been positive and recommends that no major water resource planning efforts be undertaken in the future without a commitment to the use of systems techniques.