Cyanobacterial blooms are increasingly frequent in aquatic habitats globally, driven by a complex interaction of ecological variables. This chapter addresses the key ecological forces that lead to bloom production, persistence, and toxicity. Nutrient enrichment, especially excess nitrogen and phosphorus from anthropogenic sources, is recognized as a crucial component driving cyanobacterial development. Additionally, physical variables such as water temperature, stratification, and hydrodynamics play key roles in shaping bloom dynamics. Rising global temperatures and changed precipitation patterns related to climate change further increase bloom occurrences. Light availability and competition with other phytoplankton species also impact cyanobacterial dominance, favoring species with effective light-harvesting systems. Biological interactions, including grazing pressure from zooplankton and microbial community dynamics, impact bloom growth and collapse. Furthermore, cyanobacteria adopt different adaptation techniques, such as buoyancy control, toxin synthesis, and nitrogen fixation, which boost their survival and competitive advantage. Understanding these ecological factors is crucial for anticipating and controlling blooms, as well as influencing management measures for lowering fertilizer inputs, enhancing water quality, and minimizing ecosystem disturbances.