Insects belong to the largest phylum, namely, Arthropoda in the animal kingdom. Members of this phylum are characterized with a segmented body, three pairs of jointed legs, and an exoskeleton composed of chitin. This phylum came out as the most successful group among animals because of their morphological peculiarities, high adaptability, and a wider range of distribution. However, some insects are harmful to humans as disease vectors while others are capable of human envenomation. Insects belonging to the orders such as Mantodea, Phthiraptera, Hemiptera, Coleoptera, Hymenoptera, Lepidoptera, Diptera, and Siphonaptera are well known to produce toxins. Insect toxins can be peptides, polyamines, lipids, etc., that have different modes of action and varied pathogenic intensities. Insect toxins target nervous system, muscles, and circulatory system of the victims. Aquatic coleopterans like water beetles inject a poison, whereas terrestrial beetles like blister beetles excrete irritants which can cause irritation and blistering upon contact with the human body. Venom of ants, bees, and wasps are also known to cause pain and inflammation in the locally affected areas. Saliva of parasitic insects contains certain proteins which causes allergic reactions in the host. Hence, multiple bites and stings of these insects cause inflammatory reactions such as anaphylactic shock. Also, larvae of a number of species of moths and butterflies have venomous setae or bristles over the body that causes burning sensation and temporary redness as a result of anti-inflammatory reactions. The present chapter discusses diversity of insect toxins and its effect in the biological regime.