This is the official repository for Citation Style Language (CSL) styles. An interface for browsing, searching, and filtering the styles from this repository can be found at http://www.zotero.org/styles.
Help adding new styles and updating existing ones. To contribute a (modified) style, make sure it validates and meets our style requirements, and follow the instructions for submitting styles. For translating CSL locale files, see the wiki of the CSL locales repository.
If you find editing CSL styles too difficult, you can put in a style request instead.
If you have problems using CSL styles (like getting an error when you try to install a style), contact the support of the software program you're using. While you are welcome to use the Zotero forums for general CSL support, it is not the place to ask for help with other products like Mendeley or Papers. In your bug report, clearly indicate the version of the software you're using, and mention which style is giving you problems. If you are using a style you customized yourself, make sure it validates, and make it available online (e.g., via http://gist.github.com/) so people can try to reproduce the problem.