LaTeX is a (and probably the most) popular macro package for TeX, providing many basic document formating commands extended by many of the packages included in this current list.

There is a wide variety of third-party documentation of LaTeX, and the project itself provides documentation of user commands, font selection and control, class and package writing, configuration options and modification of LaTeX. The authors are LaTeX Team and Leslie Lamport. See also latex2e-help latex209.