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The purpose of this review is to describe the development and function of the parathyroid gland from fish to mammals. We describe the molecular mechanisms regulating parathyroid gland embryogenesis and the clinical syndromes related to mutations in control genes.Recent studies have shown that fish express parathyroid hormone. This is contrary to the long held view that the earliest animals to possess parathyroid hormone were amphibians. Two fish species have been demonstrated to express parathyroid hormone but the source and physiological function of this peptide in fish remains to be determined. There is strong recent evidence that regulation and development of the parathyroid gland in mammals is controlled by a cascade of genes. A number of these regulatory factors have been identified using genetically modified mouse models or as genes causing human disease. These include, Gcm2/GCMB, Pax1 and Pax9, Hox3a, Tbx1, GATA3, TBCE, Sox3, Eya1 and Six1/4. Expression of a number of these factors occurs in the gill in fish.The function of parathyroid hormone and the parathyroid gland in humans is to regulate serum calcium levels to maintain homeostasis. Parathyroid hormone genes are present in fish but their function remains to be elucidated. Parathyroid development is regulated by a cascade of genes, which are now being rapidly defined in mouse models and in human mutations.