Sleep apnea is a sleep disorder characterized by pauses in breathing during sleep. This study will compare the use of eszopiclone to placebo for subjects with mild to moderate obstructive sleep Apnea syndrome (OSAS). Frequency and duration of apnea and hypopnea episodes, oxygen saturation, objective sleep parameters and safety information will be collected in this study. 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.