This invention relates to novel derivatives of 4-hydroxybutyric acid andprodrugsthereof, and pharmaceutically acceptable salts of the foregoing. Thisinvention alsoprovides pharmaceutical compositions comprising a compound of this inventionandthe use of such compositions in methods of treating narcolepsy, fibromyalgia,otherdisorders or conditions that are beneficially treated by improving nocturnalsleep or byadministering sodium oxybate.