Download

Microsoft Windows, Apple Mac OS X, Linux including Ubuntu:

The comprehensive cross-platform LaTeX distribution TeX Live can be downloaded here: http://www.tug.org/texlive/

Microsoft Windows only:

A long-year Windows-specific LaTeX distribution is MiKTeX. It can be downloaded via http://miktex.org

In general:

TeX and LaTeX software and packages can be downloaded from http://ctan.org