The ligand binding domain (LBD) of the nicotinic acetylcholine receptor has served as a prototype for understanding molecular recognition in the family of neurotransmitter‐gated ion channels. During the past fifty years, studies progressed from fundamental electrophysiological analyses of ACh‐evoked ion flow, to biochemical purification of the receptor protein, pharmacological measurements of ligand binding, molecular cloning of receptor subunits, site‐directed mutagenesis combined with functional analysis and recently, atomic structural determination. The emerging picture of the nicotinic receptor LBD is a specialized pocket of aromatic and hydrophobic residues formed at interfaces between protein subunits that changes conformation to convert agonist binding into gating of an intrinsic ion channel. © 2002 Wiley Periodicals, Inc. J Neurobiol 53: 431–446, 2002