Bioactive cyclic imine toxins constitute a growing family of structurally related marine neurotoxins of Dinoflagellate origin contaminating Shellfish. This chapter considers the chemistry of cyclic imine toxins, their origin, metabolism, toxicology, pharmacology, and methods developed for their detection. The main characteristic of the class of phycotoxins is represented by an imine moiety as a part of a bicyclic ring system. Spiro-prorocentrimine, a polar lipid-soluble toxin isolated from a laboratory-cultured benthic Prorocentrum species of Taiwan, presents a very different structure compared to the other classes of cyclic spiroimines. Synthetic strategies have been developed over the time to bring solutions for the important challenges associated with the complex structure of cyclic spirotoxins. With the exception of prorocentrolide congeners and spiro-prorocentrimine, most of the cyclic imine toxins were first discovered in contaminated Shellfish before the producers were identified as being dinoagellates. The benthic habitat of the dinoflagellates may account for the absence of reports regarding the presence of cyclic imine toxins in Shellfish.