Cyanobacteria are procariotic organisms (like bacteria) that are long living on Earth (about 3.5 billion years). These tiny creatures have adapted to several kinds of habitats and climates showing a huge adaptive irradiance. Their huge plasticity makes them a successful organism, able to colonise different habitats and climates. They can be found both in terrestrial and aquatic ecosystems, from poles to deserts and from lakes to the seas over the world. Another remarkable characteristic of cayanobacteria is their capacity to produce several bioactive compounds, such as toxins and allelochemicals, which makes them even stronger competitors. Cyanobacterial blooms have been considered a serious problem in lakes and reservoirs world-wide, threatening wild life, cattle and humans as well. This book covers a series of up-to-date topics in cyabobacterial research, such as the role of cyanotoxins in species interactions, toxicology and ecotoxicology, risk assessment and management of toxic cyanobacteria and cyanotoxins.