We analyze how directors with financial expertise affect corporate decisions. Using a novel panel data set, we find that financial experts exert significant influence, though not necessarily in the interest of shareholders. When commercial bankers join boards, external funding increases and investment-cash flow sensitivity decreases. However, the increased financing flows to firms with good credit but poor investment opportunities. Similarly, investment bankers on boards are associated with larger bond issues but worse acquisitions. We find little evidence that financial experts affect compensation policy. The results suggest that mandating financial expertise on boards may not benefit shareholders if conflicting interests (e.g., bank profits) are neglected.JEL classifications: G21, G24, G32, G34, G38