This paper presents a model in which politicians can increase the probability of election by making exaggerated claims about the benefits of their own platform — referred to as positive campaigning — and by exaggerating the undesirable characteristics of their rival — i.e., negative campaigning. Such lies may be detected at some point in the future and thus result in a costly loss in reputation. Thus the politician must tradeoff immediate benefits against potential future costs. Of course this problem is similar to any commercial endeavor — a car maker, for example, is tempted to claim that his car is better and the competition's is worse than it is. But it is shown that the lack of transferable property rights to political office makes lying more likely in political markets. It is also shown that there is a natural tendency for politicians to engage in more negative campaigning.