Noonan syndrome (NS) is an autosomal dominant disorder with vast heterogeneity in clinical and genetic features. Various symptoms have been reported for this abnormality such as short stature, unusual facial characteristics, congenital heart abnormalities, developmental complications, and an elevated tumor incidence rate. Noonan syndrome shares clinical features with other rare conditions, including LEOPARD syndrome, cardio-facio-cutaneous syndrome, Noonan-like syndrome with loose anagen hair, and Costello syndrome. Germline mutations in the RAS-MAPK (mitogen-activated protein kinase) signal transduction pathway are responsible for NS and other related disorders. Noonan syndrome diagnosis is primarily based on clinical features, but molecular testing should be performed to confirm it in patients. Due to the high number of genes associated with NS and other RASopathy disorders, next-generation sequencing is the best choice for diagnostic testing. Patients with NS also have higher risk for leukemia and specific solid tumors. Age-specific guidelines for the management of NS are available.