Neutral networks or sets consist of all genotypes with a given phenotype. The size and structure of these sets has a strong influence on a biological systems robustness to mutations, and on its evolvability, the ability to produce phenotypic variation, in the few studied cases of molecular phenotypes, the larger this set, the greater both robustness and evolvability of phenotypes. Unfortunately, any one neutral set contains generally only a tiny fraction of genotype space. Thus, current methods cannot measure neutral set sizes accurately, except in the smallest genotype spaces.