Trace amines (TAs) are endogenous compounds that are related to biogenic amine neurotransmitters and are present in the mammalian nervous system in trace amounts. Although their pronounced pharmacological effects and tight link to major human disorders such as depression and schizophrenia have been studied for decades, the understanding of their molecular mode of action remained incomplete because of the apparent absence of specialized receptors. However, the recent discovery of a novel family of G-protein-coupled receptors (GPCRs) that includes individual members that are highly specific for TAs indicates a potential role for TAs as vertebrate neurotransmitters or neuromodulators, although the majority of these GPCRs so far have not been demonstrated to be activated by TAs. The unique pharmacology and expression pattern of these receptors make them prime candidates for targets in drug development in the context of several neurological diseases. Current research focuses on dissecting their molecular pharmacology and on the identification of endogenous ligands for the apparently TA-insensitive members of this receptor family.