The purpose of this study is to evaluate the efficacy, safety and tolerability of aclidinium bromide doses compared with placebo in the treatment of moderate to severe, stable chronic obstructive pulmonary disease. The study will be 56 weeks in duration; a 2-week run-in period followed by a 12-week double-blind, placebo-controlled treatment period. This will be followed by an open-label 40-week treatment period and a 2-week follow up phone call. All patients will receive the higher Aclidinium Bromide during the 40-week open label treatment period.