This report reviews the existing evidence relating to the impact of uniformed women peacekeepers – i.e. military or police – in UN peacekeeping operations (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. 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 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, and between troop-contributing countries, with South–South cooperation and mentoring a particular priority.