The aim of this paper is to summarise and review all studies that have examined potential adverse health effects of passive exposure from inhaling e-cigarette vapour. Research objectives were to describe 1) the absolute impact of passive exposure from inhaling vapour when compared with background, and 2) the relative impact of passive exposure from inhaling vapour when compared with passive exposure from inhaling conventional cigarette smoke. The systematic review, which included 16 studies, found that those passively exposed to the vapours of e-cigarette users are exposed to numerous pollutants at levels above background and at concentrations that are associated with potential adverse health effects. The risk from being passively exposed to e-cigarette vapour is likely to be less than the risk from passive exposure to conventional cigarette smoke.