The Swiss Parliament is distinguished in historical international comparison by its tradition of non-professional public service. Although existing literature on interest groups (IGs) mainly treats the influence and pressure they have placed upon members of parliament (MPs), for Switzerland – particularly in light of this non-professional public service tradition – it also appears warranted to study ties between IGs and MPs. These ties, however, whether in the form of MPs being full-time employees or leading members (but not employees) of interest groups, have so far not been studied systematically. This analysis investigates the evolution of these ties from 1970 to 2010. Taking as a point of departure the increased professionalization of the Swiss Parliament, especially due to the intro- duction of permanent and specialized committees and increased compensation for parliamentary work since the beginning of the 1990s, we find that the number of MPs who are also full-time employees of IGs has steadily decreased since the 1990s. The number of MPs serving as outside or “honorary” board members of IGs has, however, actually increased since the beginning of the 1990s. This also reflects the increased importance of the Parliament in the Swiss political system, which gives interest groups with an increased incentive to develop ties to MPs. At the same time, our results show that public IGs now have more MPs as board members than do traditionally corporatist IGs.