Global plankton communities are vital to food web dynamics, ecosystem functioning, and the global cycling of carbon, nutrients, and oxygen. Modern-day ocean acidification, climate warming, and human activity are leading to shifts in the geographic distribution (i.e., biogeography) of these organisms globally, with ramifications for biogeochemical cycles. Recent in situ and remote sensing work has highlighted a poleward migration among some species and modeling studies suggest a decline in global biodiversity by the end of the century. Such changes may have occurred in the paleontological record, providing key context for modern-day understanding and future prediction. We invite contributions that use observations and models to investigate the physiological, chemical, biogeochemical, and/or physical processes controlling and driving changes in plankton biogeography on intra-seasonal to interglacial timescales. Topics may include: mechanistic drivers of lateral shifts in species distribution past and present, impacts of community shifts (physical or phenological) on carbon cycling as well as on upper trophic levels, insights from paleontological proxies, effects of changing biodiversity on ecosystem dynamics, and projected biological responses to a changing climate. Studies that make use of cross-disciplinary approaches are particularly encouraged.