This report reviews the existing evidence relating to the impact of uniformed women peacekeepers – i.e. military or police – in UN peacekeeping operations (PKOs). First, it lists the arguments most commonly used to advocate for increasing women’s participation in PKOs. The central focus of these arguments is that increasing the number of women in a PKO will improve the operational effectiveness of the mission. Thus, the dominant form of argumentation is instrumentalist: deploying more women peacekeepers is seen as necessary to achieve a more successful mission, and not as an end in itself. There then follows a closer examination of these arguments, focusing on (i) the available evidence for these claims, and (ii) the assumptions underlying them. The report contends that many of the claims justifying women’s increased participation in PKOs are at present inflated – unsurprisingly so, given the still extremely small presence of uniformed women personnel in these missions – and are based on “affirmative gender essentialisms”. Finally, there is a brief discussion of whether the current attempts to increase women’s participation in PKOs amount to “selling” gender or selling it out. The report concludes that more systematic research is needed to examine the ways in which women peacekeepers contribute to the operational effectiveness of peacekeeping missions, and how these contributions differ (or not) from the performance of male peacekeepers. It recommends financial and logistical support for mentoring programmes, both within troop-contributing countries that send all-women or mixed units into the field (so that returning women peacekeepers’ experiences are properly utilised), and between troop-contributing countries, with South–South cooperation and mentoring a particular priority.