Knuth began T_{E}X because he had become annoyed at the declining quality of the typesetting in volumes I-III of his monumental "The Art of Computer Programming".
In a manifestation of the typical hackish urge to solve the problem at hand once and for all, he began to design his own typesetting language.
He thought he would finish it on his sabbatical in 1978; he was wrong by only about 8 years. The language was finally frozen around 1985.
[Guy Steele]? happened to be at Stanford during the summer of 1978, when Knuth was developing his first version of T_{E}X. When he returned to MIT that fall, he rewrote T_{E}X's I/O to run under ITS?.

The first version of T_{E}X was written in the [SAIL programming language]? to run on a PDP-10 under Stanford's [WAITS operating system]?.
For later versions of T_{E}X, Knuth invented the concept of literate programming, a way of producing compilable source code and high quality cross-linked documentation (typeset in T_{E}X of course) from the same original file.
The language used is called WEB? and produces programs in the Pascal programming language.
The ultimate reference works for T_{E}X are the first two volumes of Knuth's [Computers and Typesetting]?, The T_{E}Xbook and T_{E}X: The Program (which includes the complete documented source code for T_{E}X).

Though well-written, T_{E}X is so large (and so full of cutting edge technique) that it is said to have unearthed at least one bug in every Pascal system it has been compiled with. T_{E}X runs on almost all operating systems.

T_{E}X is a noteworthy example of freely shared but high-quality software.
The license of T_{E}X allows free distribution and modification but demands that any changed version not be called T_{E}X, TeX, or anything confusingly similar, providing rights similar to those of a trademark.
Knuth offers monetary awards to people who find and report a bug? in it.
The award per bug started at one cent and doubled every year until it was frozen at its current value of $327.68.
This has not made Knuth poor, however, as there have been very few bugs and in any case a cheque proving that the owner found a bug in T_{E}X is usually framed instead of cashed.

The name T_{E}X is intended to be pronounced "tekh", where "kh" represents the sound at the end of Scotish "loch" (the X is meant to be the Greek letter χ).
The name is properly typeset with the "E" below the baseline; systems that do not support subscript layout use the approximation "TeX".
Fans like to proliferate names from the word "T_{E}X" - such as TeXnician (user of T_{E}X software), TeXhacker (T_{E}X programmer), TeXmaster (competent T_{E}X programmer), TeXhax, and TeXnique.

Several document processing systems are based on T_{E}X, notably
LaTeX (Lamport T_{E}X), which incorporates document styles for books, letters, slides, etc., and adds support for referencing and automatic numbering of sections and equations,
jadeTeX which uses T_{E}X as a backend for printing from James' [DSSSL Engine]?,
and Texinfo?, the GNU documentation processing system.
Numerous extensions to T_{E}X exist, among them BibTeX? for bibliographies (distributed with LaTeX), PDFTeX?, which provides T_{E}X output in Adobe Systems' Portable Document Format, and Omega, which allows T_{E}X to use the Unicode character set. All T_{E}X extensions are available for free from CTAN?, the Comprehensive T_{E}X Archive Network.

- Metafont?

*References:*

- The T
_{E}X users group: http://www.tug.org - Comprehensive T
_{E}X Archive Network: http://www.ctan.org. Repository of the T_{E}X source and hundreds of add-ons and style files. - The LaTeX project: http://www.latex-project.org.
- Donald E. Knuth,
*The T*, Reading, Massachusetts: Addison-Wesley, 1984_{E}Xbook