Aflatoxins are a group of related toxic secondary metabolites, which are produced by various species of Aspergillus. These mycotoxins have shown toxicity at various levels in different groups of organisms especially animals such as birds and mammals, and exhibit carcinogenic, mutagenic and teratogenic properties in addition to toxicity. Aflatoxin-caused-toxicity, aflatoxicosis affects liver severely and its acute condition leads to loss of appetite, lethargy and other symptoms, which ultimately result into the death. Amongst different known aflatoxins, aflatoxin B1, B2, G1 and G2 are the prominent, of which aflatoxin B1 is the most potent toxin. At molecular level, aflatoxins react with nucleic acid and proteins, and interfere with the normal functioning of the cell. The occurrence of aflatoxins is rampant due cosmopolitan distribution of their producer fungi. Considering their harmfulness and widespread nature, studies are undertaken to address aflatoxins related problems world over. This paper gives an overview of the aflatoxins and their types, synthesis, and effect on various groups of organisms.