Compact Disc ReWritable (CD-RW) is a rewritable optical disc format. Known as CD-Erasable (CD-E) during its development, CD-RW was introduced in 1997. While a prerecorded compact disc has its information permanently stamped into its polycarbonate plastic substrate, a CD-RW disc contains a phase-change alloy recording layer composed of silver, indium, antimony and tellurium. An infra-red laser beam is employed to selectively heat and melt the crystallized recording layer into an amorphous state or to anneal it at a lower temperature back to its crystalline state. The different reflectance of the resulting areas make them appear like the pits and lands of a prerecorded CD.

A CD-RW recorder can rewrite 700 mebibyte of data to a CD-RW disc roughly 1000 times. CD-RW recorders can also write CD-R discs. Except for the ability to completely erase a disc, CD-RWs act very much like CD-Rs and are subject to the same restrictions; i.e., they can be extended, but not selectively overwritten, and writing sessions must be closed before they can be read in CD-ROM drive or players. The Universal_Disk_Format 1.5 file system allows CD-RWs to be randomly rewritten, but limits disc storage capacity to roughly 530MB.

Written CD-RW discs do not meet Red Book or Orange Book Part II standards for prerecorded or recordable CDs (e.g. reduced signal levels). Consequently, CD-RWs cannot be read in CD-ROM drives built prior to 1997. CD-R is considered a better technology for archival purposes as disc contents cannot be modified and manufacturers claim greater longevity.

CD-RW discs need to be blanked before reuse. Different blanking methods can be used, including full blanking in which the entire surface of the disc is cleared, and fast blanking in which only meta-data areas are cleared: PMA, TOC and pregap, comprising a few percent of the disc. Fast blanking will obviously be much quicker, and is usually sufficient to allow rewriting the disc. Full blanking removes traces the former data for example for confidentiality.

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