Saturation mutagenesis, or site saturation mutagenesis (SSM), or simply site saturation, is a random mutagenesis technique used in protein engineering, in which a single codon or set of codons is substituted with all possible amino acids at the position. There are many variants of the site saturation technique, from paired site saturation (saturating two positions in every mutant in the library) to scanning single-site saturation (performing a site saturation at each site in the protein, resulting in a library of size 20n, where n is the number of peptides in the protein, or n-site saturation, where n sites in a peptide would be site saturated, with a library size of 20n, where if the length of your peptide is n, a complete randomization is obtained.