GNU/Linux 是個作業系統：一個能讓您與電腦互動並且執行其他程式的系統。

作業系統由許多基礎程式組成，它們是讓電腦接受使用者指令並與之溝通的必要程式；讀取資料或將其寫入硬碟、磁帶或印表機；控制記憶體的使用；以及執行其它軟體。作業系統最重要的部分是核心。在 GNU/Linux 系統中，就是以 Linux 為核心。而系統的其他部分則是由其他程式組成，這些程式主要由 GNU 計畫所提供，或者是針對 GNU 計畫所編寫的。因為單獨的 Linux 核心不能成為一個可以正常工作的作業系統，所以我們更傾向使用 “GNU/Linux” 一詞來表達人們常用的 “Linux”。

GNU/Linux 是以 Unix 作業系統為原型。從一開始，它就被設計為一個多工、多使用者的系統。這些特點使 GNU/Linux 不同於其它知名的作業系統。事實上，GNU/Linux 比您想像的更加不同。對比其他作業系統，沒人擁有 GNU/Linux，大部分的開發工作都是由無償的志願者所完成。

GNU/Linux 濫觴於 1984 年。當時，自由軟體基金會(Free Software Foundation) 開始發展自由的類 Unix 作業系統，名為 GNU。

The GNU Project has developed a comprehensive set of free software tools for use with Unix™ and Unix-like operating systems such as GNU/Linux. These tools enable users to perform tasks ranging from the mundane (such as copying or removing files from the system) to the arcane (such as writing and compiling programs or doing sophisticated editing in a variety of document formats).

While many groups and individuals have contributed to GNU/Linux, the largest single contributor is still the Free Software Foundation, which created not only most of the tools used in GNU/Linux, but also the philosophy and the community that made GNU/Linux possible.

Linux 核心 (kernel) 的首次面世是在 1991 年。當時，名為 Linus Torvalds 的芬蘭資訊科學系學生在 Usenet 新聞群組 comp.os.minix 上發佈了一種替代 Minix 核心的早期版本。請參考 Linux International 的 Linux 歷史。

Linus Torvalds continues to coordinate the work of several hundred developers with the help of a number of subsystem maintainers. There is an official website for the Linux kernel. Information about the linux-kernel mailing list can be found on the linux-kernel mailing list FAQ.

GNU/Linux users have immense freedom of choice in their software. For example, they can choose from a dozen different command line shells and several graphical desktops. This selection is often bewildering to users of other operating systems, who are not used to thinking of the command line or desktop as something that they can change.

GNU/Linux is also less likely to crash, better able to run more than one program at the same time, and more secure than many operating systems. With these advantages, Linux is the fastest growing operating system in the server market. More recently, Linux has begun to be popular among home and business users as well.