Degeneration of the cholinergic system is considered to be the underlying pathology that results in the cognitive deficit in Alzheimer's disease. This pathology is thought to be linked to a loss of signaling through the cholinergic M 1 -muscarinic receptor subtype. However, recent studies have cast doubt on whether this is the primary receptor mediating cholinergic-hippocampal learning and memory. The current study offers an alternative mechanism involving the M 3 -muscarinic receptor that is expressed in numerous brain regions including the hippocampus. We demonstrate here that M 3 -muscarinic receptor knockout mice show a deficit in fear conditioning learning and memory. The mechanism used by the M 3 -muscarinic receptor in this process involves receptor phosphorylation because a knockin mouse strain expressing a phosphorylation-deficient receptor mutant also shows a deficit in fear conditioning. Consistent with a role for receptor phosphorylation, we demonstrate that the M 3 -muscarinic receptor is phosphorylated in the hippocampus following agonist treatment and following fear conditioning training. Importantly, the phosphorylation-deficient M 3 -muscarinic receptor was coupled normally to G q/11 -signaling but was uncoupled from phosphorylation-dependent processes such as receptor internalization and arrestin recruitment. It can, therefore, be concluded that M 3 -muscarinic receptor–dependent learning and memory depends, at least in part, on receptor phosphorylation/arrestin signaling. This study opens the potential for biased M 3 -muscarinic receptor ligands that direct phosphorylation/arrestin-dependent (non-G protein) signaling as being beneficial in cognitive disorders.