REBOL is a messaging language for distributed Internet applications that run across all devices. It is pronounced like the word "rebel".

REBOL was designed over a 20 year period by Carl Sassenrath, the system architect responsible for the world's first multitasking multimedia operating system (OS), the Commodore Amiga OS. The first REBOL implementation was released in 1997 to a small group of users running on three OSs, and today REBOL has grown to reach more than 1,000,000 users running on more than 40 OS platforms.

REBOL is not a traditional computer language like C, BASIC, or Java. Instead, it was designed to solve one of the fundamental problems in computing: the exchange and interpretation of information between distributed computer systems. REBOL accomplishes this through the concept of relative expressions, which is how REBOL got its name as the Relative Expression-Based Object Language. Relative expressions, also called "dialects", provide greater efficiency for representing code as well as data, and they are REBOL's greatest strength. For example, REBOL can not only create a graphical user interface in one line of code, but it can also send that line as data to be processed and displayed on other Internet computer systems around the world.

REBOL's consistent architecture provides powerful range of abilities, from its small kernel interpreter (REBOL/Core) up to an entire Internet Operating System (REBOL/IOS).

On this page, categories are arranged in two groups and levels: 1) Top group: issues which scope extends beyond this category and topic, but which directly involves it and is important. 2) Bottom group: issues specific to this language, with their own directory category.