There is growing research on voting behavior in referendums. However, the dynamics of opinion formation in popular referendums, referendums initiated by the electorate to approve or reject decisions made by representative bodies, has not yet been studied. This is especially unfortunate as voting decisions in popular referendums differ from those in other referendums in interesting ways. Opinion formation can be a very dynamic process in popular referendums, making the referendum campaign crucial. This paper studies the dynamics of opinion formation in popular referendums and relates them to particular characteristics of the campaigns and the issues at hand. Based on the literature, we considered the effects of the intensity of the yes and no campaigns, familiarity with the issue, and partisan cues. Our study uses content analysis data and data from public opinion surveys dealing with various popular referendums held in the Netherlands. The study revealed several factors that contributed to the volatility of opinions in the referendum campaigns: the issue (new and did not fit traditional political schemes), lack of support from societal and community organizations for the position of the local authorities, and low profile campaigns on the part of local authorities. While some of these factors are general and may play a role in referendums everywhere, some can be considered ‘typically Dutch’, related to the characteristics of popular referendums in the Netherlands and the country’s political system.