Expert clinical investigators present their best and most reliable methods for the molecular diagnosis of common genetic disorders. The methods—organized by disease or diagnostic area—are robust and reproducible. They contain not only essential day-to-day benchtop wisdom and instruction, but also offer possibilities for introducing new molecular genetic diagnostic tests, as well as invaluable advice on controls, quality standards, and interpretation. Among the genetic diseases discussed are Duchenne/Becker muscular dystrophy, familial adenomatous polyposis, X-chromosome inactivation, Prader-Willi and Angelman syndromes, Huntington's disease, myotonic dystrophy, fragile X disease, cystic fibrosis, familial hypochloresterolemia, and the hemoglobinopathies.