Despite the central role of the Swiss parliament and its members in political decision-making, we know only little about what determines the latter's decisions when voting on bills. Drawing on both theoretical and empirical work carried out in other contexts, mostly in the United States, our study wishes to answer two main questions: - what is the respective role of personal political preferences, party pressure, and constituency preferences in explaining the voting decisions of members of parliaments (MPs) in the Swiss Lower House? - and to what degree do MPs in the Swiss lower house engage in strategic voting when considering bills with various options in complex voting agendas? The starting point of the research project is the large theoretical and empirical literature on MPs' voting behaviour in the United States. The personal political preferences, the influcence of party discipline, and the effect of constituency have been studied as the main factors explaining vote choices by MPs. Our project aims to assess for the first time the influence of the above factors on the voting behaviour of Swiss MPs by testing several hypotheses drawn from the literature: First, we expect that the effect of constituency preferences on MPs' voting decisions is larger for those elected under plurality rule and those who benefited more strongly from preferential votes to get elected. Second, we expect that an MPs voting behaviour is affected by the way in which she or he was selected by a party to get on the party list. Third, we assume that the effect of MPs' constituency preferences vary, depending on the type of vote in parliament. Some authors have suggested that votes in parliament also serve for position taking. We assume thus that the influence of constituency preferences is larger in published voting records than in non published votes. In addition to these hypotheses, we are also interessted in a particular type of behaviour of MPs: We wish to assess how their voting behaviour is affected by complex agenda-structures and to which degree they engage in strategic voting behaviour. We assume that MPs with a longer tenure and those which have dealt with a bill in a committee are more likely to engage in strategic voting in parliament. The ongoing project contributes in a significant way to our knowledge of how MPs decide in Swiss parliament. It yields important insights on the functioning of the particular swiss democracy and its parliament that is still defined as a "militia" parliament.