This paper presents a short summary of the knowledge on marine biotoxins. As toxins are known for their acute effects, they have been classified here according to the effects they cause in acute human poisoning incidents. Toxins may thus be distinguished into those that affect the nervous system (paralytic and other neurotoxins), memory (amnesic poisons), and the digestive system (diarrhetic toxins). Furthermore, newly emerging toxins, such as ciguatoxins or shark toxins, and factors that lead to the introduction of toxins in new areas, are presented. Relevant suggestions for further reading are given.