This Paper analyzes motives for multiple board memberships of executives and supervisory board members and their impact on firm performance using a sample of the biggest German companies between 1996 and 2006. Our empirical analysis reveals two key findings. Supervisory boards with external executives from comparable industries seem to have a positive impact on firm performance. Moreover multiple directorships of union representatives on the supervisory board are related with weaker firm performance. Several other forms of personal linkages between companies have no significant effect on firm performance, when we control for firm fixed-effects.