This study is a multicenter, randomized, modified-blind, double-dummy two-week parallel-group efficacy and safety study of arformoterol tartrate inhalation solution twice daily, tiotropium inhalation powder once daily and arformoterol tartrate inhalation solution twice daily and tiotropium inhalation powder once daily (dosed sequentially) in subjects with COPD. This study was previously posted by Sepracor Inc. In October 2009, Sepracor Inc. was acquired by Dainippon Sumitomo Pharma., and in October 2010, Sepracor Inc's name was changed to Sunovion Pharmaceuticals Inc.