Science and its practical application have brought many benefits to society but have also at times been a source of profound social harm. This has particularly occurred when the uses of scientific knowledge have strayed outside the ethical boundaries of society, or escaped lawful political control.

Military technologies have proven to be among the most difficult applications of science to control. Today's shield can become tomorrow's sword, either in our own hands or in those of an adversary. The device one person or nation builds in order to protect, another may use to coerce - or when that fails, to destroy. Advances in modern weaponry, far from making war obsolete or more humane, have only increased its potential violence.

Among all weapons, weapons of mass destruction are especially abhorrent to the conscience of humanity. A category that includes nuclear explosives, radiological and chemical toxins, and biological agents, these weapons cannot, by their very nature, reliably discriminate between either combatants and civilians on the one hand, or belligerent and neutral countries on the other. Far more than conventional weapons, they can destroy the ecological foundation upon which any future peace could be built, and harm generations far into the future. Their destructive effects are disproportionate to any legitimate or rational military objective, and escalate the probability and violence of future conflicts in incalculable ways.

For this reason, whether used to coerce or to overtly destroy, these weapons can never serve justice. As the International Court of Justice has recognized, their overt use would be incompatible with the slowly but steadily expanding fabric of humanitarian law that constrains the violence of war. Further, their use as a coercive instrument offers potent political and military rationalizations for compensatory efforts by other states, factions within them, or non-state actors, diminishing the security of all.

The use of biological and chemical weapons is banned under international law, and legal regimes outlawing their possession, with verification measures adopted or under development, are widely adhered to, including by the major powers. But there is as yet no comparable global and explicit prohibition on use of nuclear weapons, and the Nonproliferation Treaty prohibition on possession, while applying to almost all states, does not reach the most powerful, who have not fulfilled their legal obligations to negotiate effective measures relating to cessation of the arms race and the elimination of nuclear weapons.

Yet nuclear weapons remain in many ways the most dangerous of all weapons of mass destruction. In defiance of their disarmament obligations based on the Nonproliferation Treaty and other international law, and ignoring the requirements of humanitarian law, the states which possess them continue to insist on their prerogatives to retain, produce, and further develop these weapons, as well as to use them in battle.

It is to the completion of this unfulfilled obligation that this pledge is especially addressed. Where nations and institutions lag behind, individuals can and must lead.

The continuing presence of nuclear weapons in the world's arsenals casts a dark shadow on humanity's hopes for the new millennium, and on the scientific community itself. In the United States alone, tens of thousands of scientists and engineers work on nuclear weapon systems, for the most part in powerful, semiautonomous institutions that effectively shape government policy in favor of continued and increased reliance on these terrible weapons. While these scientists and engineers hold a variety of personal views regarding disarmament, their participation gives to these institutions and their political advocates the power to perpetuate the continued maintenance and development of weapons of mass destruction. Regardless of their individual beliefs, each one of these scientists and engineers becomes a tacit supporter of nuclear weapons and other weapons of mass destruction.

Scientists may do research without the ability to know or control how their work might be used. This is especially true for military related science and technology. In most science, presumed benefit is likely to outweigh lack of perfect foresight. In the case of weapons of mass destruction, it does not. We therefore call on scientists and engineers to recognize their moral obligations as global citizens to exercise due diligence regarding the potential applications of their research to the further development, testing, production, maintenance, targeting, or use of nuclear and other weapons of mass destruction. Under established principles of international humanitarian law, willful ignorance or blind obedience in such matters do not by themselves constitute a plausible defense against the assignment of responsibility for crimes carried out with such weapons.

Nowhere on earth are more resources being devoted to developing, producing, and maintaining weapons of mass destruction than in the United States. In the U.S., new uses for nuclear weapons are being examined, new doctrines for nuclear weapon use are being developed, modified nuclear weapons with significantly-improved military capabilities are being designed and deployed, and the budget for research, development, testing, and production of nuclear weapons is approaching an all-time high. But while the U.S. continues to outspend all the other nuclear weapons states in developing new infrastructure for nuclear weapons development, the others have not been idle. In fact, nuclear weapons are now increasing in legitimacy, sophistication, and importance in some if not all of the nuclear weapon states. Additionally, other nations continue to remain outside the biological and chemical weapons conventions.

A decade after the end of the Cold War, as the assumptions underlying the perverse logic of mutually assured destruction crumble, the U.S. is putting forward new justifications for maintaining and modernizing its nuclear arsenal. There is an increasing emphasis on "counterproliferation," a doctrine that contemplates nuclear retaliation and even preemptive attacks against potential users of chemical or biological weapons. Thus the deadly cycle of deterrence feeds on itself, and, as nuclear, chemical and biological weapons spread, everyone everywhere becomes less secure.

Scientists and engineers embody traditions that are rooted in the devotion to truth and the enhancement of human dignity. As a human being, one cannot ignore the ethical responsibilities inherent in every aspect of life, including one's work. In taking this pledge, scientists and engineers categorically forswear work on weapons of mass destruction in all their forms, as a step toward ensuring that their talents and energies are devoted, not to the destruction of life, but to its protection and enhancement.