Targeted deletion of metabotropic glutamate receptor–subtype 1 (mGluR1) gene can cause defects in development and function in the cerebellum. We introduced the mGluR1α transgene into mGluR1-null mutant [mGluR1 (–/–)] mice with a Purkinje cell (PC)–specific promoter. mGluR1-rescue mice showed normal cerebellar long-term depression and regression of multiple climbing fiber innervation, events significantly impaired in mGluR1 (–/–) mice. The impaired motor coordination was rescued by this transgene, in a dose-dependent manner. We propose that mGluR1 in PCs is a key molecule for normal synapse formation, synaptic plasticity, and motor control in the cerebellum.