LATEX, written as LaTeX in plain text, is a document preparation system for the TeX typesetting program.
It offers programmable desktop publishing features and extensive facilities for automating most aspects of typesetting and desktop publishing, including numbering and cross-referencing, tables and figures, page layout, bibliographies, and much more. LaTeX was originally written in 1984 by Leslie Lamport and has become the dominant method for using TeX—few people write in plain TeX anymore. The current version is LaTeX2ε. Both LaTeX and TeX are free software.
LaTeX is based on the idea that authors should be able to concentrate on writing within the logical structure of their document, rather than spending their time on the details of formatting. It encourages the separation of layout from content, whilst still allowing manual typesetting adjustments where needed. Because the author specifies the logical structure of the document, and lets the LaTeX system worry about the presentation, it is often regarded as superior to word processors and most other desktop publishing systems, which allow trivially easy visual layout changes but tend to intertwine content and form so tightly that consistency and automation are often difficult. LaTeX also provides great flexibility in formatting while maintaining the identity of structure, which purely structural systems like SGML and XML do not directly address.
LaTeX can be arbitrarily extended by using the underlying macro language for developing custom formats. For example, there are numerous commercial implementations of the whole TeX system (which includes LaTeX), and vendors may offer extra features like phone support and additional typefaces.
LaTeX is distributed under a free software licence, the LaTeX Project Public License (LPPL). The LPPL is not compatible with the GNU General Public License, as it requires that modified files indicate that they have been modified in some way; this was done to ensure that files that depend on other files will produce the expected behavior and avoids problems similar to DLL hell. The LPPL is DFSG compliant since its version 1.3.