Environmental characteristics of conceptual fusion-reactor systems based on magnetic confinement are examined quantitatively, and some compar isons with fission systems are made. Fusion, like all other energy sources, will not be completely free of environmental liabilities, but the most ob vious of tnese -tritium leakage and activation of structural materials by neutron bombardment -are susceptible to significant reduction by ingenuity in choice of materials and design. Large fusion reactors can probably be designed so that worst-case releases of radioactivity owing to accident or sabotage would produce no prompt fatalities in the public. A world energy economy relying heavily on fusion could make heavy demands on scarce nonfuel materials, a topic deserving further attention. Fusion's potential environ mental advantages are not entirely "automatic" -converting them into prac tical reality will require emphasis on environmental characteristics throughout the process of reactor design and engineering. The central role of environmental impact in the long-term energy dilemma of civilization jus tifies the highest priority on this aspect of fusion.