The genes responsible for hereditary cancers such as retinoblastoma, colorectal cancer and breast cancer have been identified through application of positional cloning from human molecular genetics. Linkage analysis is a powerful method to locate a disease gene, however a precise genetic model, detailing the mode of inheritance, gene frequencies and penetrance, is required for parametric methods, but not for nonparametric methods. The nonparametric methods ignores unaffected people, and looks for alleles that are shared by affected individuals within nuclear families as well as extended families. Hence the methods usually have been performed to identify disease genes in many hereditary diseases. In this paper, we describe the rationale and strategy of linkage analysis in detail for genetic mapping of hereditary cancers.