Recent advances in molecular genetics in hereditary hypomagnesemia substantiated the role of a variety of genes and their encoded proteins in human magnesium transport mechanisms. This knowledge on underlying genetic defects helps to distinguish different clinical subtypes and gives first insight into molecular components involved in magnesium transport. By mutation analysis and functional protein studies, novel pathophysiologic aspects were elucidated. For some of these disorders, transgenic animal models were generated to study genotype-phenotype relations and disease pathology. This review will discuss genetic and clinical aspects of familial disorders associated with magnesium wasting and focuses on the recent progress that has been made in molecular genetics. Besides isolated renal forms of hereditary hypomagnesemia, the following disorders will also be presented: familial hypomagnesemia with hypercalciuria and nephrocalcinosis, hypomagnesemia with secondary hypocalcemia, Ca2+/Mg2+-sensing receptor-associated disorders, and disorders associated with renal salt-wasting and hypokalemic metabolic alkalosis, comprising the Gitelman syndrome and the Bartter-like syndromes.