A LaTeX package that facilitates the kind of theorem setup typically needed in American Mathematical Society publications. The package consists of the theorem setup of the AMS document classes (amsart, amsbook, etc) encapsulated in LaTeX package form so that it can be used with other document classes. If you have a standard installation of LaTeX, you should find that amsthm is already present because it is included in the AMS-LaTeX distribution. The ntheorem package may also be of interest as an alternative. The author is American Mathematical. See also amslatex.