The transient receptor potential melastatin-3 (TRPM3) channel belongs to the family of transient receptor potential (TRP) cation channels that are expressed in a variety of tissues and cell types, including dorsal root ganglia, cardiomyocytes and pancreatic beta-cells. Although its natural ligands are currently unknown, TRPM3 channels can be activated by the neurosteroid pregnenolone sulfate, the synthetic ligand CIM0216, and by noxious heat. TRPM3 channels are regulated by phosphoinositides, and perhaps by calmodulin. Stimulation of TRPM3 induces an intracellular signaling cascade involving a rise in intracellular Ca2+, activation of the protein kinases Raf, ERK and JNK, and the activation of the stimulus-responsive transcription factors AP-1, CREB, Egr-1, and Elk-1. Functionally, stimulation of TRPM3 channels is connected with heat sensation by somatosensory neurons, insulin secretion by pancreatic beta-cells, regulation of neurotransmitter release, iris constriction, and tumor promotion. With the development of highly specific activators and inhibitors of TRPM3 channels, we expect that additional tissue-specific functions of TRPM3 channels will be discovered, establishing TRPM3 channels as a new therapeutic target.