The nicotinic acetylcholine receptor (nAChR) is an agonist-regulated ion-channel complex responsible for rapid neurotransmission. The vertebrate nAChR, assembled from five homologous subunits, penetrates the synaptic membrane. Different subunit combinations lead to receptor subtypes with distinctive pharmacological profiles. In comparison with mammalian nAChRs, the insect receptor is poorly understood relative to functional architecture and diversity. Several genes for Drosophila, Locusta and Myzus encoding insect nAChR subunits have been identified, although the functional assembly and presence of different subtypes of these receptors are not defined. The insect nAChR is the primary target site for the neonicotinoid insecticides, thereby providing an incentive to explore its functional architecture with neonicotinoid radioligands, photoaffinity probes and affinity chromatography matrices. This review considers the current understanding of the structure and diversity of insect nAChRs based mainly on recent studies in molecular biology and protein biochemistry.