Assuming random mating and random sampling of pedigrees, the likelihood of a set of pedigree data is developed in terms of: (1) the population distribution of the different genotypes; (2) the phenotypic distributions for the different genotypes, and (3) the genotypic distribution of offspring given the parents’ genotypes. This last is given for any number of unlinked autosomal loci, two linked autosomal loci, an X-linked locus, and combinations of these possibilities. Methods are given for using this likelihood to test specific genetic hypotheses and for genetic counsellin