Is there any reason not to spy on other people as necessary to get the facts straight, especially if you can put the facts you uncover to good use? To “spy” is secretly to monitor or investigate another's beliefs, intentions, actions, omissions, or capacities, especially as revealed in otherwise concealed or confidential conduct, communications and documents. By definition, spying involves secret, covert activity, though not necessarily lies, fraud or dishonesty. Nor does spying necessarily involve the use of special equipment, such (...) as a tape recorder or high-powered binoculars. Use of a third party agent, such as a “private eye” or Central Intelligence Agency operative is not necessary for surveillance to count as spying. Spying is morally troublesome both because it violates privacy norms and because it relies on secrecy and, perhaps, nefarious deception. Contemporary technologies of data collection make secret, privacy-invading surveillance easy and nearly irresistible. For every technology of confidential personal communication - telephone, mobile phone, computer email - there are one or more counter-technologies of eavesdropping. But covert surveillance conducted by amateur and professional spies still includes old-fashioned techniques of stealth, trickery and deception known a half century ago: shadowing by car, peeking at letters and diaries, donning disguises, breaking and entering, taking photographs, and tape recording conversations. The ethical examination of spying cannot be reduced to a conversation about reigning in the mischief potential of twenty-first century technology. We do need to concern ourselves with what tomorrow's spies will do with nanotechnology, but plenty of spying is possible with the time-tested techniques of the Baby Boomers, or even, for that matter, the Victorians. The philosophical problem I wish to consider here is the ethical limits of spying on others, when the reasons for spying are good. I explore the plausibility of three interrelated ideas. The first idea is one I will call the anti-spying principle: spying on other adults is prima facie unethical. The second idea is an exception to the anti-spying principle: spying on others is ethically permissible, even mandatory, in certain situations, where the ends are good. The third and final idea is a constraint on exceptions to the anti-spying principle: where spying is ethically permitted or required, there are ethical limits on the methods of spying. The virtuous spy will violate privacy and transparency norms, of course; but he or she will, to the extent possible, continue to act with respect for the moral autonomy and for the moral and legal interests of the investigative target. (shrink)