This chapter develops a political competition model in which campaign platforms are partially binding. A candidate who implements a policy that differs from his/her platform incurs a cost of betrayal, which increases with the size of the betrayal. I assume that voters are uncertain about candidates’ policy preferences. The model can also explain political polarization in which extreme candidates win an election in the following manner. If voters believe that a candidate is likely to be extreme, there is a semi-separating equilibrium: an extreme candidate imitates a moderate one, with some probability, and approaches the median policy with the remaining probability. Although an extreme candidate will implement a more extreme policy than will a moderate candidate, regardless of imitation or approach, partial pooling ensures that voters prefer an extreme candidate who does not pretend to be moderate over an uncertain candidate who announces an extreme platform. As a result, a moderate candidate never has a higher probability of winning as opposed to an extreme candidate.