Many marine invertebrates produce potent toxins, turning themselves poisonous as a defense strategy against predators. The chemical structures of marine toxins in general—and Maitotoxin (MTx) in particular—are very interesting and represent a formidable challenge for organic synthesis. The appearance in the literature of the structure of brevetoxin-B awoke a large interest in synthetic organic chemists. In the case of the synthesis of the ring systems of MTx, the stereoselectivity was accomplished by state transition chelation. In some cells such as skin broblasts, MTx seems to activate large conducting channels leading to cell lysis. The accompanying polyepoxide process proposed for marine polyether ladder toxins has clear precedents in several reports on epoxide and cycle formation during antibiotic polyether biosynthesis. MTx has attracted much attention given its powerful bioactivity involving disruption of Ca2+ homeostasis. MTx is not only one of the most potent toxins, but it also possesses multiple activities that appear to be linked to elevation of intracellular Ca2+ concentration.