Surveillance matters. Chapter 1 shows we are today watched more closely than at any time in modernity. Philosophers have long speculated that just feeling watched might change our behaviour, but empirical evidence for this is limited. This thesis extends the evidence by exploring ‘the watching eyes effect’ – a phenomenon identified by psychologists which suggests that the presence of pictures of eyes can trigger us to feel more watched and act more prosocially. The research presented also tests the effect of the ‘mere presence’ of a camera. In Chapter 1 we see that there is significant evidence that we are hypersensitive to gaze and feeling watched. However, a laboratory study reported in Chapter 2 finds no effect of eye cues or the presence of a camera on prosociality. In Chapter 3 a systematic review of the available watching eyes literature develops the hypothesis that if, as others suggest, watching eyes cue us to feel watched and worry about our reputation we might find they have more consistent effects on antisocial behaviour. A meta-analysis of 15 experiments supports this contention, finding a 35% reduction in antisocial behaviour when eye cues are present. Seeking to explore this further, Chapter 4 reports three studies finding that eye cues (or a camera) do not reduce antisocial behaviour in the laboratory. Chapter 5 reports the results of a field study finding consistent reductions in crime at 9 locations where signs are erected – three of which are statistically significant with crime falling 27%, 100%, and 100%. Chapter 6 reports a carefully designed large-scale field experiment in the London Borough of Ealing. Unexpectedly, over the twelve months after we put the signs up there was no cycle crime for 6 months preventing meaningful assessment of the signs’ effectiveness. In concluding, we consider the possibility that our laboratory studies show participants don’t feel watched in the presence of eye cues or a camera – that the watching eyes effect is the result of false positives and publication bias. However, noting Chapter 1’s evidence for our hypersensitivity to surveillance, and our findings in Hereford this investigation concludes that perhaps more consistent watching eyes effects can be found in the field than in the laboratory. In the end, having synthesised the psychological and interdisciplinary evidence for surveillance effects and added its empirical findings to the canon, this thesis advances us towards a psychology of surveillance, and points the way to further research.