(±)-2-Amino-4-phosphonobutyric acid (AP4) is a glutamate analogue widely used in neuroscience and biochemical research as a selective agonist for group III metabotropic glutamate receptors (mGluR4, mGluR6, mGluR7, and mGluR8). These receptors modulate synaptic transmission and neurotransmitter release, particularly in the hippocampus, cerebellum, and other brain regions. It is employed to study the roles of these receptors in synaptic plasticity, neuroprotection, pain modulation, epilepsy, and psychiatric disorders such as schizophrenia, anxiety, depression, and addiction. Researchers use it to block or activate specific glutamatergic pathways, aiding in understanding excitotoxicity, learning, memory, and neurodegenerative conditions like Parkinson’s disease. Additionally, it serves as a tool in electrophysiological and behavioral studies to explore therapeutic targets for neurological and psychiatric disorders.