DeCSS is a computer program capable of decrypting content on a commercially produced DVD video disc. Before the release of DeCSS, there was no way for computers running the GNU/Linux operating system to play video DVDs.
DeCSS was developed without a license from the DVD CCA, the organization responsible for DVD copy protection — namely, the Content-Scrambling System (CSS) used by commercial DVD publishers. The release of DeCSS resulted in a Norway criminal trial, resulting in acquittal, of one of the authors of DeCSS; and the DVD CCA launched numerous lawsuits in the United States in an effort to stop the distribution of the software.