Parties and Information Processing of Party Followers in Swiss Referendums Cognitive psychology differentiates between the systematic and the heuristic type of information processing. Research on Swiss referendums has demonstrated that cognitively demanding heuristics are rarely used. Even party slogans are hardly ever considered in making voting decisions – and only a fraction of the voting populace even knows them. However, that does not mean that Swiss voters systematically process political information. Empirical research shows that in spite of their lack of knowledge of party slogans party followers routinely vote in accordance with them. On the basis of an analysis of two similar referendums the article discusses explanations for this phenomenon. Systematic reception of arguments often depends on heuristics such as party support whereas systematic processing of content often takes place under the guidance of a preferred party.