Phytoplankton are responsible for half of the photosynthesis on the planet. Forming the base of marine food webs, phytoplankton also play a critical role in the global carbon cycle, regulating climate over geological timescales through the sequestration of atmospheric carbon dioxide. These diverse and remarkable microorganisms are in constant dialogue with their surroundings, responding to fluctuating resource availability (i.e. nutrients and light), neighboring microbiota and predation pressure from viruses and grazers over spatial and temporal scales. We explore how phytoplankton live and die in these dynamic ocean environments, with the goal of understanding the microscale interactions that shape primary production and biogeochemical cycling in the global ocean. Our research utilizes a combination of laboratory, field-based and computational approaches to explore natural phytoplankton assemblages across diverse marine environments, from coastal waters to the open ocean.