<p>Plastic pollution is a growing environmental crisis, with plastic waste accumulating across marine, freshwater, and terrestrial ecosystems. While early research focused on the transport and deposition of plastic debris, recent studies highlight the role of environmental forces in fragmenting plastics into secondary microplastics. However, the spatial variability and drivers of plastic fragmentation remain poorly understood. Here, we introduce the concept of <i>the geography of plastic fragmentation</i>, a transdisciplinary framework that integrates natural and social science perspectives to examine the intrinsic (e.g., polymer composition, design, and prior weathering) and extrinsic (e.g., hydrodynamics, climate, land use) controls on fragmentation processes. We propose a research agenda that includes mapping fragmentation hotspots, conducting field experiments across environmental gradients, developing integrative modeling approaches, and leveraging spatial management strategies to mitigate secondary microplastic release. We argue that applying a geographical perspective to plastic fragmentation can help bridge critical knowledge gaps, providing insights into where, when, and how plastics fragment across diverse environments. By synthesizing geomorphological, socio-economic, and policy dimensions, this approach can inform targeted interventions, from product design improvements to waste management reforms. Advancing research on the geography of plastic fragmentation is essential for shaping effective mitigation strategies and guiding sustainable plastic policies in the face of the predicted increase in plastic production and ongoing climate change.</p>