This chapter contains information on various anticholinergic agents that block the stimulation of muscarinic receptors by acetylcholine. These include solanaceous alkaloids as well as various types of synthetic anticholinergic agents that are used as antispasmodics, antiulcer agents, mydriatics, and cycloplegics. The structure‐activity relationships of various agents, biocomparative methods for pharmacological evaluation, and their users are also discussed.