Th is paper deals with shareholder activism by institutional investors and the scope of their duties to people who commit their savings to undertakings for collective investments. It argues, that due to their unique position within the structure of the corporate decisionmaking process and their fi duciary duties to funds’ participants on one hand and their portfolio companies on the other, asset managers should actively use their voice in corporate aff airs, and do so taking the public interest into account. Th e article sets out with description of changes in ownership structure of public corporations, which led to the unprecedented rise in the infl uence of asset managers on contemporary capital markets. Then, it discusses recent regulatory initiatives to impose a duty to engage in corporate matters on institutional investors. Next part reconstructs three arguments, most commonly deployed in the public debate, in favor of imposing the duties related to institutional investors’ engagement: them being the „owners” of the companies; the fiduciary nature of their relationship to both their portfolio companies and their investors; as well the belief – for which I propose the name of the Spiderman doctrine – that one’s responsibility should be proportionate to one’s power.