Purpose: Firm innovation is relevant in the fast paced business world. Recent years, research on board diversity has found that demographic and cognitive diversity have an impact on innovation, however this research is still inconclusive. To contribute to the research this thesis introduces informal hierarchy as a moderating variable to investigate if this can explain the previous contradictory findings.  Theoretical perspective: By using concepts from resource dependence theory, upper echelons theory, and behavioral theory, five hypotheses were formulated and tested.  Method: For board diversity Blau’s index was used, innovation was defined as an index of strategic change and informal hierarchy was measured as the dispersion of rank within the board, through the gini coefficient. 186 Swedish publicly listed limited liability firms were analyzed. Findings: The results provided evidence that neither demographic nor cognitive board diversity impacts innovation and informal hierarchy does not have a moderating role on that relationship. However, the findings suggest a direct relationship between informal hierarchy and innovation. Another finding suggests that board size and informal hierarchy separately has a negative impact on innovation, however when both board size and informal hierarchy is present there is a slightly positive effect on innovation.