This paper develops a theoretical model of informative campaigning, both positive and negative. We argue that some information on a candidate can be transmitted more efficiently by his opponents and that negative campaigning, on average, facilitates a more informed choice by the electorate. In our model, voters have incomplete information about candidates' qualities. Each candidate can either lead a positive campaign, defined as issue-focused, indicating his high quality, or a negative campaign, defined as revealing detrimental information about his competitor. Voters receive the information that candidates choose to reveal and rationally update their beliefs about the remaining issues. We derive the equilibrium behavior of candidates in this framework and compare it to stylized facts of negative campaigning reported in the empirical literature.