First, technology is moving forward, making strategic defenses appear to be a more cost effective option than there were in the 1960s. Second, were we able to obtain a significant advantage over the USSR in strategic defenses, we could have a substantial measure of strategic superiority over them. Third, if both sides deploy significant strategic defense capabilities, the nature of the offensive force balance will become even more important than it is today; in particular, strategic force vulnerabilities that are worrisome today could prove disastrous for stable deterrence in a world that includes robust strategic defenses. Fourth, this picture would be sharply changed should strategic defenses themselves prove vulnerable, for this might create the first strike in space that would decisively alter the balance of forces on earth. Fifth, strategic defenses are likely to call NATO's strategy of diliberate nuclear escalation into even deeper question than it is today. The U.S. R&D program should be based on three criteria: First, our program should hedge against a Soviet breakout of the ABM Treaty and--in the longer term--against Soviet deployment of space-based defensive systems. Second, we should be looking for weapons concepts that will provide for quantum increases in capability and quantum reduction in cost. Finally, our technology programs need to be conducted with a view toward survivable defenses, especially for their spacebased components.