Objective: To review the pharmacology, pharmacokinetics, efficacy data, and adverse effects of eszopiclone in the treatment of transient and chronic insomnia in adult and geriatric patients. Data Sources: A MEDLINE literature search (1966–May 2005) was conducted to retrieve articles and abstracts involving eszopiclone. The manufacturer of the drug provided a general summary of clinical data and abstracts of unpublished Phase III clinical trials. Study Selection and Data Extraction: All articles identified from the data sources were reviewed, and information deemed relevant was included for this review. Data Synthesis: Food and Drug Administration approval of eszopiclone was based on 6 double-blind, placebo-controlled trials. Five trials published in abstract or study form were reviewed. The sixth trial was not available for evaluation. An open-label continuation trial was also reviewed. All studies showed statistically significant improvements in sleep parameters in adult and elderly patients treated for insomnia with eszopiclone. CONCLUSIONS: The results of the 5 available double-blind, placebo-controlled studies (and 1 open-label, 6-month extension) showed that eszopiclone was safe and effective in the treatment of transient and chronic insomnia in adult and geriatric patients. Tolerance with long-term exposure (6 mo) and rebound insomnia were not observed. The results of the 6-month, open-label extension trial demonstrated that improvements in sleep parameters were sustained. Future studies comparing eszopiclone with other non benzodiazepine sedative–hypnotics (eg, zolpidem, zaleplon) are needed with cost data to clearly define the role of eszopiclone in the pharmacotherapy of chronic insomnia.