With TeX, Knuth designed a formatting system that is able to produce a large range of documents typeset to extremely high quality standards. For various reasons (e.g. quality, portability, stability and availability) TeX spread very rapidly and can nowadays be best described as a world-wide de facto standard for high quality typesetting. Its use is particularly common in specialized areas, such as technical documents of various kinds, and for multi-lingual requirements.
The TeX system is fully programmable. This allows the development of high-level user interfaces whose input is processed by TeX's interpreter to produce low-level typesetting instructions; these are input to TeX's typesetting engine which outputs the format of each page in a device-independent page-description language. The LaTeX system is such an interface; it was designed to support the needs of long documents such as textbooks and manuals. It separates content and form as much as possible by providing the user with a generic (i.e. logical rather than visual) mark-up interface; this is combined with style sheets which specify the formatting.
Recent years have shown that the concepts and approach of LaTeX are now widely accepted. Indeed, LaTeX has become the standard method of communicating and publishing documents in many academic disciplines. This has led to many publishers accepting LaTeX source for articles and books; and the American Mathematical Society now provides a LaTeX package making the features of AmSTeX available to all users of LaTeX. Its use has also spread into many other commercial and industrial environments, where the technical qualities of TeX together with the concepts of LaTeX are considered a powerful combination of great importance to such areas as corporate documentation and publishing. This has also extended to on-line publishing using, for example, PDF output incorporating hypertext and other active areas.
With the spreading use of SGML-compliant systems (e.g. Web-based publishing using HTML or XML) TeX again is a common choice as the formatting engine for high quality typeset output: a widely used such system is The Publisher from ArborText, whilst a more recent development is the object-oriented document editor Grif. The latter is used for document processing in a wide range of industrial applications; it has also been adopted by the Euromath consortium as the basis of their mathematician's workbench, one of the most advanced of the emerging project-oriented user environments. Typeset output from SGML-coded documents in these systems is obtained by translation into LaTeX, which will therefore soon also be a natural choice for the output of DSSSL-compliant systems.
Because a typical SGML Document Type Definition (DTD) uses concepts similar to those of LaTeX, the formatting is often implemented by simply mapping document elements to LaTeX constructs rather than directly to `raw TeX'. This enables the sophisticated analytical techniques built into the LaTeX software to be exploited; and it avoids the need to program in TeX.