Sex remains one of the most salient demographic dividing points in American politics today. President Obama has women, particularly unmarried women, to thank for his re-election victory. The gender difference in voter support for the Democratic and Republican presidential candidates grew from twelve points in 2008 to eighteen points in 2012. This gender gap in candidate preference likely emerges because of gender gaps in policy preferences. Yet despite much scholarly and popular interest in this topic, the cause or causes of gender gaps in policy preference remain unclear. The Political Battle of the Sexes: Exploring the Sources of Gender Gaps in Policy Preferences examines gender gaps in policy preferences in the United States, outlines their form, and explores their causes. This work makes four contributions to the literature on gender gaps. First, it provides the first comprehensive look at gender gaps across time and various issue areas completed since the 1980s. Second, it provides a theoretical framework for explaining the causes of gender gap emergence that incorporates both nature (biology) and nurture (socialization) and provides the basis with which to predict the attitudes on which gender gaps will likely emerge. Third, it explores the causes of gender gaps in foreign and social policy, two of the policy domains where gender gaps continue to increase. Finally, it introduces a new way of conceptualizing biology based on emerging research in the hard sciences. Studying gender gaps remains difficult. Women comprise a very diverse group, and are divided by far more factors than the sex categorization that unites them. However, electoral realities demand that scholars studying political behavior pay attention to sex based differences in political preferences. Women exhibit consistent preference tendencies relative to men, and women remain more likely to show up on Election Day than men. As such, gender gaps have substantial political and practical implications for women in the United States. And while explaining their causes requires drawing from a wide array of fields, ranging from biology to economics, understanding the origins and consequences of gender gaps does much to further empirical research in public opinion and mass behavior.