UK TeX FAQ -- question 256

### Getting `\marginpar` on the right side

In `twoside` documents, LaTeX makes sterling attempts to put `\marginpar`s in the correct margin (the outer or the gutter margin, according to the user's command). However, a booby-trap arises because TeX runs its page maker asynchronously. If a `\marginpar` is processed while page n is being being built, but doesn't get used until page n+1, then the `\marginpar` will turn up on the wrong side of the page. This is an instance of a general problem: see "finding if you're on an odd or an even page".

The solution to the problem is for LaTeX to 'remember' which side of the page each `\marginpar` should be on. The mparhack package does this, using marks stored in the `.aux` file.

`mparhack.sty`
  macros/latex/contrib/supported/mparhack.tar.gz