In recent years the field of corporate governance has been characterized by an increasing effort to gain a better understanding of the role of boards for the financial performance of a firm. The present study thereby searches to build upon the small but growing literature that focuses particularly on boards in a two-tier system. It extends the current knowledge about the effectiveness of supervisory boards by measuring the interaction of board work and firm performance and illustrates the differences and similarities between the one-tier and the two-tier system in this context. It moreover highlights the advantages of testing board effectiveness in a dualistic system and enriches our current understanding on how various board characteristics at once impact the financial performance of a firm. (authors' abstract) / Series: Working Papers / Institute for Strategic Management