Harmful Algal Blooms (HABs) have multiple negative impacts on the exploitation of living marine resources, other socio-economic activities, public health, and dynamics of marine ecosystems. The increase in the intensity and frequency of these events requires the application of adequate environmental management measures, including the prediction of HAB and eventual mitigation of its effects. This course covers relevant topics related to the physiology and ecology of HAB-forming organisms in marine ecosystems, including functional traits, environmental drivers and triggers, distribution patterns, and temporal trends. The effects of natural and anthropogenic-driven environmental changes (e.g., eutrophication, climate variability) will be specifically explored. The consequences of HAB events on human and ecosystem health and services, including the fate of phycotoxins in aquatic systems, along with the methodological strategies used for quantifying HAB-forming species and phycotoxins, will be further explored. This information will be integrated into the context of HAB modeling and prediction, including case studies of operational early warning systems. This 30-hour online, mostly synchronous course, includes theoretical sessions, with discussion fora, practical sessions, and a final assessment test. Participants are expected to have an academic background in Marine Sciences.