While negative campaigning has received increased attention, scholars have mostly focused on its effects. Studies looking at the determinants of negative campaigning remain sparse. Our article contributes to literature by developing a two-level model that takes into account the strategic choices of political actors and their characteristics as well as the context in which the negative strategy takes place. We apply our model to a rich data set of newspaper ads regarding direct democratic votes held in Switzerland. Our results show that negative campaigning, as measured by personal attacks, is more likely if political actors defend the status quo or are lagging behind in the polls, if the ad stems from a populist right party or entails no explicit endorsement, or if the ballot day draws near. Popular initiatives and more intense campaigns also generate a higher share of negative campaigning. Overall, then, a number of causal factors identified in (U.S.) elections also matter in Swiss direct democracy, which suggests that the reasons that make political actors willing to ‘‘go negative'' are of broad relevance.