Debian 是一个 GNU/Linux 的发行版。我们稍后将会详细地讨论什么是发行版
第 1.5 节 “发行版的角色”。但是当前情况下，我们暂且将其简单地归纳为一个完整的操作系统，包括软件和系统的安装及管理，所有的这些都基于 Linux 内核和自由软件（尤其是来自 GNU 项目的自由软件）。
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
第 1.3.3.1 节 “Existing Debian Sub-Projects and Blends”, dedicated to that purpose.
这些 Debian 的组成部分由定义清晰的框架组织而成，保证“子发行版”之间互相兼容、互不干扰。它们全部采用一致的方案发布新版本。同时它们都基于相同的基础构建而成，可以轻松地使用 Debian 仓库中的软件进行扩展、完善和个性化配置。
所有 Debian 的工具都遵循这个指导方向：debian-cd 已经存在很长时间了，它可以用来创建一组光盘，其中仅包含一系列预先选择的软件包；debian-installer 也是一个模块化的安装工具，易于适应不同的需求。APT 可以使用不同的来源安装软件包，同时保证系统整体的一致性。
Debian 遵循所有的自由软件的原则，在充分准备好之前新版本不会释出。开发者不会被时间表限定需要追赶一个随意的截止日期。人们经常抱怨 Debian 发布稳定版之间的时间间隔过长，但这样的谨慎保证了 Debian 一贯的可靠性：在赋予全发行版“稳定”标签之前长时间的测试确实是必要的。
Debian 不会在质量问题上妥协：核心软件包中众所周知严重缺陷都会在新版本中得到解决，即使需要推迟已经公布的发布日期。可选软件包的严重缺陷如果没有被修复则无法达到质量要求，因此会直接从稳定版中移除。
从法律上来说，Debian 是一个由美国的非营利志愿者协会管理的项目。这个项目大约有一千左右的 Debian 开发者，但是聚集了远超这个数的贡献者（翻译者，bug 报告者，艺术家，临时开发者等）。
为了完成使命，Debian 拥有一个巨大的基础架构，由许多赞助者提供的服务器连接在因特网上。
