‘The tragedy of the commons’ and ‘the common heritage of mankind’ are concepts that dominate the legal discourse on governing global commons, including spaces beyond national jurisdictions, essential resources, and concerns such as biodiversity conservation and climate change. This paper offers a critical account of their origins. It associates each with a prominent speech-act of the late 1960s: Garrett Hardin introduced the former to a group of scientists in 1968; Arvid Pardo articulated the latter to the First Committee of the UN General Assembly in 1967. The paper shows that that Hardin and Pardo’s interventions responded to pressing issues of the time: decolonization, developed/developing state relations, and pressures of population and resource security. Channelling that period’s fascination with integrative knowledge, they were impressive, if error-laden, feats of synthesis of economic, legal, and scientific data and theories. At the same time they had parochial, illiberal and even imperial dimensions, playing upon and exacerbating the mistrust that then typified international relations. These are all legacies we must contend with today, in our legal engagements with global commons.