Initiation Codon is the codon at which the translation of a polypeptide chain is initiated. This is generally the first AUG triplet in the mRNA molecule from 5' end, where the ribosome binds to the cap and starts to scan in a 3' direction. Though, the surrounding sequence context is significant and might lead to the first AUG being bypassed by the scanning ribosome in the favor of the alternative, downstream AUG. Also known as a "start codon". Occasionally other codons might serve as initiation codons, example UUG.