This lecture (∼ 45‐55 slides) will be aimed at senior undergraduate students and graduate students in aquatic sciences with little background in phycology. This lecture could be used in a Aquatic Ecology or Sciences (Limnology) course, an Ecology course, a Phycology course, Environmental Science.Cyanobacteria that may lead to blooms encompass a wide range of different functional groups. We will present:1) the evolutionary history of cyanobacteria (2‐3 slides) (this helps explain some of their present‐day traits)2) basic biology and physiological/ecological traits of planktonic cyanobacteria that are most often associated with visible biomass accumulations (“blooms”) in freshwater/brackish systems of various regions of the world. Traits to be considered include: capacity for N fixation, nutrient uptake and storage (C, N, P), siderochromes, buoyancy regulation (gas vacuoles, mucilage), life cycles, growth rates vs. loss rates (resistance to grazing), allelopathy (negative vs. positive biotic interactions) Functional groups. Planktonic genera may also produce toxins, contributing to harmful algal blooms. (∼12‐14 slides).3) Cyanotoxins: the principal types of toxins produced and their effects (persistence) will be compared, along with theories as to the biological function of these compounds. (∼ 6 slides)4) Specific case studies of blooms types under different climates: e.g. scum‐forming, metalimnetic, dispersed (∼6)5) The factors that appear to explain and control cyanobacterial dominance will be presented, including nutrient effects, temperature, and food chain changes. These factors vary across temporal and spatial scales. Evidence for eutrophication and climate change in mediating directly or indirectly the frequency and severity of freshwater cyanobacterial blooms will be considered (∼8‐10).6) Research avenues Controversial or unresolved topics: e.g. invasiveness?, cosmopolitan or geographically restricted (e.g. endemism? in hot spring taxa), toxin concerns and bioaccumulation), nitrogen fixation (“pretenders”), nutrient stoichiometry. Unexplored diversity at different levels (molecular, chemical, taxonomic), techniques for controlling cyanobacteria blooms, the future for cyanobacteria under climate change scenarios (∼4)7) General references, web resourcess and primary articles. (∼2)8) Questions and potential experiments for instructors and students will be provided at the end of the lecture (supplementary slides).