<p>Managing cumulative pressures on socio-ecological systems presents as one of the foremost policy challenges of our time. Climate change, invasive species, development and pollution all have the potential to individually, and collectively, degrade the earth’s natural and cultural resources. International environmental law, a crucial element of global environmental governance, has a role to play in prompting and coordinating a response to cumulative effects. Hitherto, however, international approaches have been fragmented and unfocused, further complicating the already challenging application of Cumulative Effects Assessment (CEA) at the local level. This article examines how the two primary protected area treaties—the World Heritage Convention and the Ramsar Convention on Wetlands—have evolved to address the concepts of CEA and cumulative effects. It uncovers instances of ambiguity and fragmentation in treaty guidance material and concludes with a suggestion for further empirical research into how CEA could (or should) apply in the context of internationally protected areas.</p>