The Inter-Agency Standing Committee (IASC) Gender Marker is a tool that tracks and measures whether humanitarian projects mainstream gender adequately and respond effectively to the distinct needs of women, girls, boys, and men. The Gender Marker represents an important opportunity to improve the quality of humanitarian programming by addressing gender inequality. This article explores the development, implementation, and results from the IASC Gender Marker since its initial inception in 2007, through the piloting phases in the 2009 and 2010 Consolidated Appeals Processes (CAPs), to its partial and then full implementation in 2011 and 2012, respectively.