The significance of predation by protists in aquatic microbial food webs is highlighted, emphasizing their ecological roles and the importance of phagotrophic protists. These microorganisms, ranging from 2 μm flagellates to >100 μm ciliates and dinoflagellates, exhibit various feeding strategies and trophic states. Protists are major sources of mortality for heterotrophic and autotrophic bacteria, compete with herbivorous zooplankton for phytoplankton, and influence organic sinking flux. Their excretions provide essential nutrients and trace metals. Methodological advances, such as molecular genetic analysis and flow cytometry, are facilitating research on protistan predation. The review covers the distribution and diversity of phagotrophic protists, their ecological significance, and future research directions, including the impact of cell-to-cell communication on predator-prey interactions.The significance of predation by protists in aquatic microbial food webs is highlighted, emphasizing their ecological roles and the importance of phagotrophic protists. These microorganisms, ranging from 2 μm flagellates to >100 μm ciliates and dinoflagellates, exhibit various feeding strategies and trophic states. Protists are major sources of mortality for heterotrophic and autotrophic bacteria, compete with herbivorous zooplankton for phytoplankton, and influence organic sinking flux. Their excretions provide essential nutrients and trace metals. Methodological advances, such as molecular genetic analysis and flow cytometry, are facilitating research on protistan predation. The review covers the distribution and diversity of phagotrophic protists, their ecological significance, and future research directions, including the impact of cell-to-cell communication on predator-prey interactions.