This Technical Brief collects and summarizes information on genetic tests clinically available in the United States to detect genetic markers that predispose to Dds. It also identifies, but does not systematically review, existing evidence addressing the tests' clinical utility. This Brief primarily focuses on patients with idiopathic or unexplained Dds, particularly intellectual disability, global developmental delay, and autism spectrum disorder. Several betterdefined Dd syndromes, including Angelman syndrome, fragile X syndrome, PraderWilli syndrome, Rett syndrome, RubinsteinTaybi syndrome, SmithMagenis syndrome, velocardiofacial syndrome, and Williams syndrome are also included. Patientcentered health outcomes (e.g., functional or symptomatic improvement) and intermediate outcomes (e.g., changes in clinical decisions or family reproductive decisions, the tests' diagnostic accuracy and analytic validity) are examined.