A method of mapping a population of mutant antibodies formed from a template antibody having at least one complementary determining region, said at least one complementary determining region together comprising n amino acid residues, the method comprising: a. generating a population comprising n sets of mutant antibodies, each set comprising member antibodies having X number of different predetermined amino acid residues at a single predetermined position of the at least one complementary determining region; wherein each set of mutant antibodies differs in the single predetermined position; and the number of different member antibodies generated is equivalent to n x X; b. assaying the population for at least one predetermined property, characteristic or activity; c. for each member identifying any change in said property, characteristic or activity relative to the template antibody; and d. creating a functional positional map that is used to identify one or more of: i. positions and mutations which do not affect the property, characteristic or activity of the mutant antibody compared to the template antibody; ii. fully mutable sites compared to the template antibody; and iii. positions and mutations which result in a mutant antibody with an improvement of the property, characteristic or activity compared to the template antibody, wherein X is all or a subset of the 19 amino acids not present at the single predetermined position, and the improvement is selected from reduction of protein-protein aggregation, enhancement of protein stability, increased protein solubility, increased protein pH stability, increased protein temperature stability, increased protein solvent stability, increased selectivity, decreased selectivity, introduction of glycosylation sites, introduction of conjugation sites, reduction of immunogenicity, enhancement of protein expression, increased antigen affinity, decreased antigen affinity, a change in binding affinity, a change in immunogenicity, a change in catalytic activity, pH optimization, and enhancement of specificity. a. generating a population comprising n sets of mutant antibodies, each set comprising member antibodies having X number of different predetermined amino acid residues at a single predetermined position of the at least one complementary determining region; wherein each set of mutant antibodies differs in the single predetermined position; and the number of different member antibodies generated is equivalent to n x X; b. assaying the population for at least one predetermined property, characteristic or activity; c. for each member identifying any change in said property, characteristic or activity relative to the template antibody; and d. creating a functional positional map that is used to identify one or more of: i. positions and mutations which do not affect the property, characteristic or activity of the mutant antibody compared to the template antibody; ii. fully mutable sites compared to the template antibody; and iii. positions and mutations which result in a mutant antibody with an improvement of the property, characteristic or activity compared to the template antibody, wherein X is all or a subset of the 19 amino acids not present at the single predetermined position, and the improvement is selected from reduction of protein-protein aggregation, enhancement of protein stability, increased protein solubility, increased protein pH stability, increased protein temperature stability, increased protein solvent stability, increased selectivity, decreased selectivity, introduction of glycosylation sites, introduction of conjugation sites, reduction of immunogenicity, enhancement of protein expression, increased antigen affinity, decreased antigen affinity, a change in binding affinity, a change in immunogenicity, a change in catalytic activity, pH optimization, and enhancement of specificity. i. positions and mutations which do not affect the property, characteristic or activity of the mutant antibody compared to the template antibody; ii. fully mutable sites compared to the template antibody; and iii. positions and mutations which result in a mutant antibody with an improvement of the property, characteristic or activity compared to the template antibody, wherein X is all or a subset of the 19 amino acids not present at the single predetermined position, and the improvement is selected from reduction of protein-protein aggregation, enhancement of protein stability, increased protein solubility, increased protein pH stability, increased protein temperature stability, increased protein solvent stability, increased selectivity, decreased selectivity, introduction of glycosylation sites, introduction of conjugation sites, reduction of immunogenicity, enhancement of protein expression, increased antigen affinity, decreased antigen affinity, a change in binding affinity, a change in immunogenicity, a change in catalytic activity, pH optimization, and enhancement of specificity.