Investors have increased their attempts to influence the corporate responsibility policies of the companies that they own. However, it is not clear whether these investors have sufficient influence over companies to motivate such change. This chapter assesses whether the investor engagement with GSK on developing-country access to essential medicines was effective in changing corporate policy. It concludes that there are circumstances where investors can use their influence over companies to motivate change in corporate responsibility policies, and that, in this case, investor engagement with GSK contributed very significantly to changing the company's approach to access to essential medicines. However, as the investors were responding to a high-profile campaign by Oxfam, it is questionable whether these investors would have achieved the same scale of change in the absence of such a campaign.