It is often claimed that surveillance should be proportionate, but it is rarely made clear exactly what proportionate surveillance would look like beyond an intuitive sense of an act being excessive. I argue that surveillance should indeed be proportionate and draw on Thomas Hurka’s work on proportionality in war to inform the debate on surveillance. After distinguishing between the proportionality of surveillance per se, and surveillance as a particular act, I deal with objections to using proportionality as a legitimate ethical (...) measure. From there I argue that only certain benefits and harms should be counted in any determination of proportionality. Finally I look at how context can affect the proportionality of a particular method of surveillance. In conclusion, I hold that proportionality is not only a morally relevant criterion by which to assess surveillance, but that it is a necessary criterion. Furthermore, while granting that it is difficult to assess, that difficulty should not prevent our trying to do so. (shrink)