Keep your rights by...
Keeping the copyright to your work lets you
With scholarly, peer-reviewed articles, the version of the article you can place in the repository is determined by the journal. Most journals do not allow you to deposit the final version of the article (i.e. Publisher's PDF), but many may allow other verions listed below:
Pre-print: the version of the article before it has been submitted for peer-review
Post-print: the version of the article as it was submitted for printing (after peer-review changes have been made)
Publisher's PDF: the version of the article as it appeared in the published journal
To determine what the policy is:
Other kinds of materials, such as book chapters, conference procedeeings, presentation slides, data, etc. may be deposited if you have retrained the rights to do so. If you have questions about which version may be deposited, you may email email@example.com.