There has been little theoretical debate of why companies behave in socially responsible ways whilst descriptive analysis of corporate social responsibility is flourishing. As result, there have been few methodological debates on how to study both what responsible actions are and why companies act accordingly. This methodological and theoretical essay discusses how institutional social theory has been and could be used in explaining socially responsible corporate behaviour. It is explored what kinds of theoretical tools are needed in explaining this behaviour and how various tools can be integrated into one model explaining socially responsible corporate actions. It is argued that researchers should empirically focus simultaneously on normative origins and institutional environments of responsibilities, on power relations determining the particular responsibilities, and on institutional arrangement of corporate actions.