Each installation of Zotero comes with a small selection of popular bibliographic styles. In addition, thousands of styles are readily available at the online Zotero Style Repository. Zotero makes use of the newly developed XML-based Citation Style Language (CSL) to configure citation formatting. It has been designed to be an open, robust and international-ready standard, independent of any particular application, document format, or programming language.

It is quite common to have multiple publications sharing a certain style (e.g. Nature Biotechnology uses the same bibliographic style as Nature). To avoid having numerous duplicates in the Zotero Style Repository, all of which would have to be maintained individually, Zotero supports dependent styles. A dependent style (e.g. named “Nature Biotechnology”) simply points to the more generic independent style with the same style formatting (in this case “Nature”). Nonetheless, it is easier to simply store the particular style preferences of different publications than it is to memorize them all. Thus, the Style Manager:

More than 1,100 styles are available to Zotero 2.0 users, and this is where to find new ones and make sure they're up to date. The Style Manager displays all the currently installed bibliographic styles and the date they were most recently updated. You can also add or delete styles from Zotero here. CSL style files can be added manually using the + button, or deleted with the - button. Additionally, styles can be added automatically through the “Get additional styles…” link to the Style Repository. Once there, simply find the desired style and click the “install” link. Hovering the mouse cursor over a style's name will give you a preview of that style.

If you have some technical savvy, and are not afraid to edit XML by hand, take a look at the info on creating styles, or the step-by-step guide. If on the other hand you are wary of writing your own CSL style, you can still do a lot of the upfront work in getting the style developed. There is a good chance that one of the more technically inclined members of the Zotero community will help out if you are willing to put in a bit of work to kick things off. This page should help get you started: Requesting Styles.

Further information is at the Styles FAQ, or the Styles Forum.