Debian 是一套 GNU/Linux 散佈版。我們會在
節 1.5, “散佈版的角色” 討論散佈版的定義，但不是現在，目前只須知道 Debian 是個完整的作業系統，其中包括安裝與管理所需的軟體與系統，而且全都以 Linux 核心與自由軟體 (特別是來自 GNU 專案的自由軟體) 為基礎。
When he created Debian, in 1993, under the leadership of the Free Software Foundation (
FSF), Ian Murdock had clear objectives, which he expressed in the
Debian Manifesto. The free operating system that he sought would have to have two principal features. First, quality: Debian would be developed with the greatest care, to be worthy of the Linux kernel. It would also be a non-commercial distribution, sufficiently credible to compete with major commercial distributions. This double ambition would, in his eyes, only be achieved by opening the Debian development process just like that of Linux and the GNU project. Thus, peer review would continuously improve the product.
Debian, remaining true to its initial principles, has had so much success that, today, it has reached a tremendous size. Currently, it officially supports nine hardware release architectures and several variations of each architecture known as “flavors”, and also other kernels like FreeBSD, although the FreeBSD-based ports are not part of the set of officially supported architectures either. Furthermore, with more than 31,000 source packages, the available software can meet almost any need, whether at home or in the enterprise.
The sheer size of the distribution can be inconvenient: it is really unreasonable to distribute 18 DVD-ROMs (only containing the packages qualifying as "Free Software") to install a complete version on a standard PC… This is why Debian is increasingly considered as a “meta-distribution”, from which one extracts more specific distributions intended for a particular public: Debian Science for scientific use, Debian Edu for education and pedagogical use in an academic environment, Debian Med for medical applications, Debian Jr. for young children, etc. A more complete list of the sub-projects can be found in
節 1.3.3.1, “Existing Debian Sub-Projects and Blends”, dedicated to that purpose.
這些 Debian 的分門觀係根據定義完善的框架整理而來，因此能保證這些「次散佈版」間沒有煩人的相容性問題。它們皆遵循通用的版本發行規劃。也因為基礎相同，它們皆能利用 Debian 軟體庫中收錄的應用程式輕鬆擴充、補全、與客製化。
所有的 Debian 工具以此方式運作：debian-cd 運作多時由一組 CD-ROMs 納入預選的套件；debian-installer 也是模組化安裝器，容易改裝符合特定需要。APT 從其他來源安裝套件，保證彼此的一致性。
Debian follows all of the principles of Free Software, and its new versions are not released until they are ready. Developers do not work upon a set schedule and don't have to rush to meet an arbitrary deadline. People frequently complain of the long time between Debian's stable releases, but this caution ensures that Debian's legendary reliability is met: long months of testing are indeed necessary for the full distribution to receive the “stable” label.
Debian will not compromise on quality: all known critical bugs on key packages are resolved in any new version, even if this requires the initially forecast release date to be pushed back. Optional packages whose critical bugs are not fixed, and thus do not meet the quality requirements, are simply dropped from the stable release.
就法而言，Debian 是美國非營利、志願組織的一個計畫。此計畫由數千名 Debian 發展者 組成，再加上其他貢獻者 (譯者、錯誤報告者、藝術者、插花的發展者等)。
To carry its mission to fruition, Debian has a large infrastructure, with many servers connected across the Internet, offered and hosted by many sponsors.
