What is LaTeX?
LaTeX is a document preparation system. You write plain text marked up with commands describing structure, and LaTeX typesets it into a finished PDF.
The idea in one sentence
In a word processor you decide how a heading looks; in LaTeX you saythis is a heading and the document class decides how it looks. That separation between content and presentation is the whole point, and nearly everything else about LaTeX follows from it.
What you actually write
A LaTeX document is a text file. A very small one looks like this:
\documentclass{article}
\begin{document}
\section{Introduction}
Hello, world.
\end{document}You then run a LaTeX engine over that file and it produces a PDF. The\documentclass line chooses the overall design — an article, a book, a set of slides — and the commands inside describe structure: sections, lists, figures, tables, citations.
Where the name comes from
TeX is a typesetting program written by Donald Knuth, first released in 1978, because he was unhappy with the typography of his own books. TeX is powerful but low-level. LaTeX, written by Leslie Lamport in the early 1980s, is a large set of macros on top of TeX that provides the document-level vocabulary — \section, \cite,\begin{figure} — that most people actually want. When people say they "write in LaTeX", they mean this layer.
It is pronounced LAY-tek or LAH-tek; the final letter is a Greek chi, not an English "x". Nobody will mind either way.
What it is unusually good at
- Mathematics. LaTeX's maths typesetting is its most famous feature and still the reference standard. Its notation has been adopted well beyond LaTeX itself.
- Long, structured documents. Cross-references, numbering, tables of contents and bibliographies are maintained by the system rather than by you, so they stay correct as the document moves around.
- Consistency. Because the class decides the appearance, a hundred-page document is typeset the same way throughout without anybody policing it.
- Bibliographies and citations. Reference lists are generated from a database of sources in whichever style is required.
What it is not
LaTeX is not a word processor, and it is not WYSIWYG — you do not see the finished page as you type, although most modern editors show a live preview beside the source. It is also not the right tool for everything: a short letter or a quick note is usually faster in whatever you already have open.
Engines, distributions and editors
The engine is the program that does the typesetting — pdfTeX, XeTeX and LuaTeX are the common ones, with the latter two able to use the fonts already installed on your system and to handle Unicode directly. A distribution (TeX Live, MiKTeX, MacTeX) bundles an engine with the thousands of packages that make up the wider ecosystem. An editor is where you type; that can be a dedicated LaTeX editor, a general text editor with a LaTeX extension, or a browser-based service that keeps the whole toolchain server-side.
Is it free?
Yes. TeX, LaTeX and the mainstream distributions are free and open source, and have been for their entire history. Individual packages and templates carry their own licences, which is worth checking before you reuse someone else's work — see licensing.