Phycotoxins belong to several classes of compounds: polyketides, alkaloids and amino acids. As naturally produced compounds, many enzymatic systems in nature are capable of metabolizing them. This chapter compiles information on the functional-structural characterization of marine neurotoxic phycotoxins, as well as therapeutic and medical management applied in the intoxications. Saxitoxin-group toxins are water-soluble compounds that induce paralytic shellfish poisoning in humans. Ciguatoxin-group toxins are lipid-soluble polyether compounds. Brevetoxin-group toxins are marine biotoxins, primarily produced by a dinoflagellate, Karenia brevis, which can accumulate in shellfish and fish, and cause neurotoxic shellfish poisoning. Yessotoxins are lipophilic toxins produced mainly by the dinoflagellate Protoceratium reticulatum. Palytoxin-group toxins are complex polyhydroxylate D compounds with both lipophilic and hydrophilic areas. One of the most investigated groups of toxins and the only one that produced a clinical drug are conotoxins. © 2020 John Wiley & Sons Ltd All rights reserved.