Genetic linkage analysis remains a powerful tool for identifying regions of the genome that may harbor suceptibility loci. This unit describes the traditional approach of calculating two-point and multipoint lod scores when the underlying genetic model is known. Components of the genetic model include whether a trait is dominant, recessive, or codominant, whether it is autosomal or sex linked, and whether there is mutation at the disease gene locus, as well as the disease and marker allele frequencies and the penetrance of the disease allele. The approach to genetic linkage analysis presented in this unit assumes that the markers are loosely spaced, so that there is no linkage disequilibrium between genetic markers. Practical examples and step-by-step guidelines are presented.