Inclusion Criteria

• Subject meets DSM-IV criteria for primary insomnia and reports sleeping no more than 6.5 hours per night and/or taking more than 30 minutes each night to fall asleep for at least one month prior to screening.
• Male and female subjects must be between 21 and 64 years of age, inclusive, at the time of consent.
• Female subjects of childbearing potential must sign the Women of Childbearing Potential Addendum to the informed consent form. Females considered not of childbearing potential must be surgically sterile or greater than one-year post menopausal, defined as a complete cessation of menstruation for at least one year.
• Subject must be in general good health, based on screening physical examination (including brief neurological examination), medical history, 12-lead ECG, and clinical laboratory values (hematology, serum chemistry and urinalysis).

Exclusion Criteria

• Subject has any clinically significant unstable medical abnormality, chronic disease, or a history of a clinically significant abnormality of the cardiovascular, respiratory, hepatic, or renal systems.
• Subject has a history of cancer within the past 5 years, or current malignancy except for non melanomatous skin cancer.
• Subject has a psychiatric diagnosis with psychosis, dementia or delirium. Subjects with Sexual and Gender Identity Disorders or other non-psychotic disorders will be considered on a case-by-case basis.
• Subject has one of the following Personality Disorders: schizotypal, schizoid, or borderline personality disorder.
• Subject has difficulties in sleep initiation or maintenance associated with known medical diagnosis (e.g. sleep apnea, restless leg syndrome (RLS), or periodic leg movement syndrome (PLMS), or has any condition that has or may affect sleep (e.g., chronic pain, BPH, etc.).
• Subject has participated in a previous eszopiclone clinical trial.
• Subject has a known sensitivity to racemic zopiclone, any benzodiazepine, any sedative hypnotic, any substance that is contained in the formulation, or has been hospitalized for any allergic conditions (e.g. recurrent dermatitis, drug hypersensitivity, drug allergy, etc.).
• Subject has history of substance abuse in the past 10 years or substance dependence at any time or positive urine drug test at screening .
• Subject tests positive at screening for hepatitis B surface antigen, hepatitis C antibody or has a history of a positive result.
• Subject is known to be seropositive for HIV.
• Female subjects who are pregnant, lactating or within 6 months post partum.
• Subject self-reports consumption of more than two alcoholic beverages daily, 14 or more alcoholic beverages weekly, or five or more alcoholic beverages on any given day.
• Subject has taken any psychotropic medications or other medications known to affect sleep within the 3 days prior to screening visit or is anticipated to need any of these types of medications during double-blind treatment .
• Subject has participated in any investigational study within 30 days prior to screening.
• Subject has taken herbal supplements, purported to have central nervous system effects,(tablets, powders, extracts or tinctures) or combination products with herbs or melatonin within 14 days prior to screening or St. John's Wort within 30 days prior to screening.
• Subject is a rotating or third/night shift worker.
• Subject is a staff member or relative of a staff member.