This chapter discusses the nature, toxicity, and chemistry of Paralytic shellfish toxins (PSTs), a naturally occurring family of > 50 powerful neurotoxic alkaloids, emphasizing their identification and quantification. PSTs display a remarkable structural resemblance to each other. They are causative agents of paralytic shellfish poisoning (PSP) reported globally due to shellfish consumption containing harmful PSTs. Traditionally, the presence of PSP toxin in shellfish and other sources has been determined using efficient and controversial mouse bioassay (MBA). With the advent of new technological manifestations, more reliable and quick detection methods have been developed, offering potential possibilities to solve analytical complications in the domain of marine toxins. Each approach and technique has its associated pros and cons, but their increased usage to fathom and screen the presence of PSTs has, undoubtedly, reduced the mortality rates and absolute toxication numbers over the last few decades. © 2022 selection and editorial matter, Gulzar Ahmad Nayik and Jasmeet Kour; individual chapters, the contributors.