Over the past decades, the clinical relevance and biological significance of Mg2+ have been thoroughly documented. Although multiple Mg2+-transport pathways have been biophysically characterized, the molecular identity of the postulated components of Mg2+-homeostasis regulation in vertebrates remain undefined. Recent advances in the fields of genetics, genomics and proteomics, and novel technologies such as cDNA microarrays have allowed for substantial progress in this area. The mitochondrial Mrs2 protein was the first human Mg2+ transporter characterized as such, and an important element for future analyses of the role of mitochondria in managing intracellular Mg2+. Several molecules with Mg2+ transport capabilities have been identified through a screen designed to find genes upregulated under hypomagnesic conditions. This includes SLC41A1 and 2, ACDP2 and MagT1. Finally, the elucidation of the molecular cause underlying two different hereditary diseases leading to hypomagnesemia resulted in the cloning and characterization of claudin 16 (paracellin-1), and TRPM6. Whereas claudin 16 plays a crucial role in paracellular Mg2+ transport, TRPM6 is involved in the transcellular pathway. TRPM6 and its closest relative TRPM7 are both puzzling ion channel-kinase fusions, and perhaps the most unexpected newly identified players in the regulation of Mg2+-homeostasis in vertebrates.