The chapter introduces FSTAT (Version 1.2), a computer program designed to calculate F-statistics, which are widely used by population biologists to assess genetic differentiation among populations. F-statistics include Fw (within-population heterozygote deficit), Fm (among-population heterozygote deficit), and Fst (global heterozygote deficit). The program is based on Weir and Cockerham's (1984) estimators, which are more accurate than those derived from Nei's (1977) methods, which do not account for sampling effects. FSTAT performs various statistical tests, including those for Hardy-Weinberg equilibrium and population differentiation, using a random number generator from L'Ecuyer (1988). The program is available for both real and protected modes on PC compatibles, with specific limits on the number of samples, loci, alleles, individuals, and permutations. It is distributed free of charge and can be obtained electronically or via an FTP server. The chapter also acknowledges the contributions of several researchers and the funding from various institutions.The chapter introduces FSTAT (Version 1.2), a computer program designed to calculate F-statistics, which are widely used by population biologists to assess genetic differentiation among populations. F-statistics include Fw (within-population heterozygote deficit), Fm (among-population heterozygote deficit), and Fst (global heterozygote deficit). The program is based on Weir and Cockerham's (1984) estimators, which are more accurate than those derived from Nei's (1977) methods, which do not account for sampling effects. FSTAT performs various statistical tests, including those for Hardy-Weinberg equilibrium and population differentiation, using a random number generator from L'Ecuyer (1988). The program is available for both real and protected modes on PC compatibles, with specific limits on the number of samples, loci, alleles, individuals, and permutations. It is distributed free of charge and can be obtained electronically or via an FTP server. The chapter also acknowledges the contributions of several researchers and the funding from various institutions.