This document provides an introduction to Linux. It explains that Linux is not an operating system by itself, but rather a kernel that is typically used with the GNU operating system. Linux originated from the need for an alternative to expensive UNIX systems and academically restricted MINIX. A 21-year old student named Linus Torvalds developed the initial Linux kernel for his new PC hardware and announced its development in an email in 1991. Today, Linux powers supercomputers, stock exchanges, bullet trains and more, with only 2% of its code originally written by Torvalds and the rest contributed by its vast developer community.