KNOPPIX is an operating system based on Debian designed to be run directly from a DVD, one of the first of its kind for any operating system. Knoppix was developed by, and named after, Linux consultant Klaus Knopper. When starting a program, it is loaded from the removable medium and decompressed into a RAM drive. The decompression is transparent and on-the-fly.

Although KNOPPIX is primarily designed to be used as a Live CD, it can also be installed on a hard disk like a typical operating system. Computers that support booting from USB devices can load KNOPPIX from a live USB flash drive or memory card. There are two main editions: the traditional compact-disc (700 megabytes) edition and the DVD (4.7 gigabytes) "Maxi" edition. Each main edition has two language-specific editions: English and German.

KNOPPIX mostly consists of free and open source software, but also includes some proprietary software, as long as it fulfils certain conditions. Knoppix can be used to copy files easily from hard drives with inaccessible operating systems. To quickly and more safely use Linux software, the Live CD can be used instead of installing another OS.