Knoppix, stylized KNOPPIX, is a Linux distribution based on Debian designed to be started directly from a CD / DVD. Knoppix is one of the best-known Live Distros. It was developed by Linux consultant Klaus Knopper. When starting a program it is loaded from the optical disc and decompressed into a RAM drive. The decompression is transparent and on-the-fly.

KNOPPIX is a bootable Live system on CD, DVD or USB flash drives, consisting of a representative collection of GNU/Linux software, automatic hardware detection, and support for many graphics cards, sound cards, SCSI and USB devices and other peripherals. KNOPPIX can be used as a productive Linux system for the desktop, educational CD, rescue system, or adapted and used as a platform for commercial software product demos. It is not necessary to install anything on a hard disk. Due to on-the-fly decompression, the CD can have up to 2 GB of executable software installed on it (over 9GB on the DVD "Maxi" edition).

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.