This thesis provides a literature review into the subject of the gender gap in high-­‐ ranking positions. Causes that can be categorized inside the supply side of this phenomenon will be reviewed and three different categories will be discussed: gender differences in ability, gender differences in preferences, and gender differences in perceived ability. Women tend to shy away from competition, and also underperform in competition against men. In the areas of ability, perceived ability, preferences for risk, and preferences for other regarding preferences, results are much more ambiguous. The disappearance of the gender gap in high-­‐ranking positions does not seem efficient nor welfare improving