Environmental proteomics, the study of changes in the abundance of proteins and their post-translational modifications, has become a powerful tool for generating hypotheses regarding how the environment affects the biology of marine organisms. Proteomics discovers hitherto unknown cellular effects of environmental stressors such as changes in thermal, osmotic, and anaerobic conditions. Proteomic analyses have advanced the characterization of the biological effects of pollutants and identified comprehensive and pollutant-specific sets of biomarkers, especially those highlighting post-translational modifications. Proteomic analyses of infected organisms have highlighted the broader changes occurring during immune responses and how the same pathways are attenuated during the maintenance of symbiotic relationships. Finally, proteomic changes occurring during the early life stages of marine organisms emphasize the importance of signaling events during development in a rapidly changing environment. Changes in proteins functioning in energy metabolism, cytoskeleton, protein stabilization and turnover, oxidative stress, and signaling are common responses to environmental change.