This invention generally relates to muscarinic receptor antagonists of formula (I) which are useful, among other uses, for the treatment of various diseases of the respiratory, urinary and gastrointestinal systems mediated through muscarinic receptors. Specifically, the invention relates to derivatives of azabicyclo compounds, including, for example, 6-substituted azabicyclo[3.1.0]hexanes, as well as pharmaceutical compositions containing such compounds and methods of treating diseases mediated through muscarinic receptors.