Corporations have taken on an expansive role in the global community with transnational operations, extensive resources, power and influence, and significant environmental and human rights impacts. While corporate social responsibility (CSR) has developed standards and practices aimed at addressing the social responsibility of corporations, its legal effect, if any, is unclear. In part, this can be linked to the lack of status and direct accountability for corporations in international law. This article seeks to carve out a space for corporations in which the realities of their power and impact can be acknowledged, addressed, and managed. It suggests that this can be accomplished through the recognition of corporate customary international law. This corporate customary international law would apply the well-developed law-creation processes of traditional state-based customary international law to businesses. Employing CSR as a practical example, the article suggests that not only is corporate customary international law a theoretical possibility, but its elements can already be seen in the development of CSR. Ultimately, this article aims to show how customary international law, which is an existing tool of international law formation, can be used to bridge the gap between the traditional and contemporary international systems and increase opportunities for businesses to fulfil ethical and legal obligations and to be held accountable for environmental and human rights harms.