Abstract: The present invention provides a method of producing a DNA library comprising a plurality of DNA sequences of interest, where each DNA sequence of interest has at least two predetermined positions, with at each predetermined position a codon (MAX) selected from a defined group for that position, the codons within a group coding for different amino acids.

Abstract: A set of libraries of proteins, which proteins are capable of specific binding interactions by virtue of amino acid residues at two or more determined positions including a first determined position and one or more other determined positions, which set of libraries consists of: a) 6 to 20 libraries in which each library has one or several but less than 20 amino acid residues at the said first determined position and is randomised at the said one or more other determined positions, the arrangement being such that interaction of the 6 to 20 libraries with a specific binding partner identifies an amino acid residue at the said first determined position that takes part in the specific binding interaction, and b) 6 to 20 libraries of corresponding design for each of the said one or more other determined positions. A set of libraries of genes which code for the proteins.