The defence industry makes extensive use of physicists, who devote their skills to the design of weapons of destruction, notably nuclear weapons. Such practices contribute to the further proliferation of nuclear weapons in developing countries. Physicists employed to monitor nuclear power stations have been encouraged to downplay risks or design faults in installations and to cover-up major accidents. Given the especially competitive nature of the discipline, some practitioners make unethical use of the insights and results obtained by others. Others, in pursuit of personal ambition, lend their authority to disproportionate claims for the allocation of limited resources to prestige projects in high energy physics.