Toxigenic cyanobacteria are photosynthetic prokaryotes that are most often recognized in marine and freshwater systems, such as lakes, ponds, rivers, and estuaries. When environmental conditions (such as light, nutrients, water column stability, etc.) are suitable for their growth, cyanobacteria may proliferate and form toxic blooms in the upper, sunlit layers. The biology and ecology of cyanobacteria have been extensively studied throughout the world during the last two decades, but we still know little about the factors and processes involved in regulating toxin production for many cyanobacterial species. In this minireview, we discuss these microorganisms, and more especially the toxins they produce, as a potential and important health risk for wild and domestic animals.