Organisms are known to produce compounds that play vital roles in metabolism, sustenance, growth, and development, along with toxic chemicals that have deleterious effects on living organisms. Biotoxins are toxic compounds originating from microbes, fungi, plants, and animals and pose health risks to other organisms. Biotoxins can be classified based on their chemical structures, source of origin, and mode of action. In recent years, a good amount of interest has been shown in toxinology for its multilevel role in clinical, agricultural, and even bioterrorism. Understanding the underlying mechanism of biotoxin action and its toxicity can reveal a plethora of pragmatic knowledge on the predator–prey relationship, defence mechanisms, drug discovery and therapies, food safety, and human health. The chemistry behind biotoxin reactions and remediation is sparingly known. The present knowledge of most biotoxin’s action is that it is known to exert toxicity by blocking cellular ion channels, disrupting cellular membranes, altering signalling pathways, and inhibiting proteins and enzymes. An enthralling list of biotoxins and their chemistry advances our understanding of these natural toxins and paves the way for developing novel preventive methods in the form of antidotes for better utilisation towards human health and global security. In this chapter, broad categories of biotoxins and their chemistry are evaluated, and their modes of action with implications are presented for a better understanding of biotoxins for the future beneficial role of humankind.