Overgrowth syndromes are a group of growth disorders which have gained joint attention from the fields of pediatrics, endocrinology and genetics. Major progress such as the identification of genetic causes has recently enhanced the delineation of the characteristic and non-characteristic manifestations, phenotype-genotype correlations and knowledge of the underlying pathophysiological mechanisms. As a consequence, the possibilities for distinction between the different overgrowth disorders have increased. Patients with either typical or non-typical features in whom no molecular abnormalities are found, form a basis for further research. Identification of new pathogenic alterations in these patients, best exemplified by the Marfan-related syndromes, has provided further understanding of the regulatory gene network involved. In light of recent developments and as an aid to the diagnostic process, the aim of this review is to give a comprehensive overview of the clinical, molecular genetic and pathophysiological aspects of each of the classic and new overgrowth syndromes.