This invention provides 4-amino-1-benzylpiperidine and related compounds and pharmaceutically acceptable salts thereof which are useful as muscarinic receptor antagonists. This invention also provides pharmaceutical compositions containing such compounds; processes and intermediates useful for preparing such compounds; and methods for treating disease conditions mediated by muscarinic receptors, such as overactive bladder, irritable bowel syndrome, asthma and chronic obstructive pulmonary disease, using such compounds.