Paralytic shellfish toxins (PSTs) are a large group of marine biotoxins (~50 analogues), mainly produced by marine dinoflagellates of the genera Alexandrium, Gymnodinium and Pyrodinium, which are more typical in tropical and temperate climate zones. All members of the toxin group share a common core structure. Still, the combination of different chemical functionalities defines the subgroup of each analogue (e.g., carbamoyl, N-sulfocarbamoyl, decarbamoyl, benzoyl), influencing its toxicological action and determining the level of toxicity of each member. PSTs are prone to biotransformations within living organisms, affording analogues with higher or lower toxicity. Such biotransformations may be mediated by different agents (e.g., enzymes, natural reducing agents, bacteria) in different living organisms undergoing chemical processes, leading to diverse outcomes. This work intends to highlight the main reactions (bioconversions) that occur in living organisms (dinoflagellates, bivalves, and humans) and relate changes in molecular structure, caused by such responses, to toxicity. Additionally, we also present research under development aiming to create chemical solutions for the decontamination of bivalve molluscs, thus helping to minimize this problem’s social and economic impacts.