Cyanobacterial blooms are an escalating global concern, driven by nutrient imbalances, climate change, and human activities. This chapter examines the underlying nutrient dynamics and stoichiometric principles that govern bloom formation, focusing on the critical roles of nitrogen (N) and phosphorus (P). Deviations from the classical Redfield ratio (C:N:P = 106:16:1) are explored to understand how altered nutrient stoichiometry favors bloom-forming cyanobacteria and affects toxin production. The role of micronutrients such as iron (Fe), sulfur (S), and trace metals is also discussed, particularly in relation to nitrogen fixation and bloom physiology. External nutrient inputs—via agricultural runoff, wastewater discharge, and atmospheric deposition—are identified as key contributors to eutrophication. Internal nutrient recycling, including sediment release and biomass decomposition, further sustains bloom persistence. Adaptive traits such as buoyancy regulation, nitrogen fixation, phosphorus scavenging, and resting stages enhance cyanobacterial competitiveness and promote feedback loops that reinforce bloom dominance. These blooms disrupt food webs, deplete oxygen, and produce toxins harmful to aquatic life and human health. Long-term ecosystem changes, including sediment–water nutrient fluxes and biodiversity loss, complicate recovery. Effective management requires a multifaceted approach involving nutrient reduction strategies, biological control (biomanipulation), and innovative remediation methods such as Phoslock application, floating wetlands, and emerging biotechnological tools. The chapter emphasizes the importance of integrating stoichiometric understanding with remote sensing, nutrient modeling, and ecosystem-based management. A transdisciplinary framework is essential for predicting bloom dynamics and developing sustainable solutions to mitigate their environmental and public health impacts.