We propose a model of political competition not over policy programs, but over ideologies: models of the world that organize voters’ experiences and guide the inferences they draw from observed outcomes. Policy-motivated political parties develop ideologies, and voters choose the ideology that best explains their observations. Preferences over policies are then induced by the adopted ideology. Parties thus care about winning the ideological battle, as it confers an advantage in the electoral arena. We show that in equilibrium political parties always propose different models of the world. This divergence extends to all features of the environment, not just policy dimensions. A lower degree of policy extremism in the past increases the divergence on the policy dimension, thus leading to higher ideological polarization.