It supports most things you'd want: matrices, subscripts, superscripts, blackboard bold, etc. To expand on Joe's answer, while there is no support for actual LaTeX, the LaTeX like language Joe describes is very powerful and convenient. You will need to set up and administer a web server (and most likely a database server as well) in order to use wiki software, but in the long term, and especially if you are serious about having a space to collect your stuff, this is the superior solution. I personally use Confluence, but free alternatives are available (the example that first comes to mind is MediaWiki, which powers Wikipedia, and it has comprehensive LaTeX support). That being said, if you'd like to have a note-taking application together with LaTeX mathematics, I suggest turning to a wiki software that supports advanced typeset mathematics.

The expressions are not lined with the text, so if you want to include them in a free-running text, be prepared for a major pain.

You cannot edit them once they are in place.

Formulas are read-only and appear as images.

Typeset your mathematics with it (with the registered version, it understands TeX mathmode), and drag-and-drop your equations to your OneNote notebooks.

It's commercial, but you can continue to use the evaluation version without LaTeX editing and other goodies for free after the trial period is over.

Install the MathType Equation editor ( Wikipedia description).

This applies to OneNote 2007, so if you have more recent version, it could be somewhat different. One workaround that is sort-of-kinda-working (with severe caveats), so go ahead, if you absolutely need to.

No, there's no way to include LaTeX (and I assume you mean the mathematics typeset with it) in OneNote.

Mac onenote gem