Cyanobacteria are a globally abundant bacterial phylum that make key contributions to primary production and nutrient cycling in aquatic ecosystems. However, some cyanobacteria also cause substantial adverse environmental impacts through harmful blooms and the production of potent toxins. Given their global significance, understanding the processes governing cyanobacterial ecology is critical for assessing aquatic ecosystem function. While abiotic environmental factors have traditionally been considered most important, a growing body of literature indicates that interactions with other microorganisms, in particular heterotrophic bacteria, shape cyanobacterial growth, population dynamics, and ecological success. In this review, we provide a synthesis of the importance of interbacterial interactions in controlling cyanobacterial populations and their ecological impacts on natural aquatic environments and argue that these relationships should be incorporated into conceptual and predictive frameworks of cyanobacterial ecology.