Crossref will enable registration for preprints by August 2016. Crossref's original registration policy prevented its members from registering content and assigning Digital Object Identifiers (DOIs) to "duplicative works." The new policy means that preprints will have separate DOIs from any later versions that may be registered, according to an announcement from the organization.
Preprint is a term that has several meanings, but in the proposal adopted by Crossref's Board of Directors it will be defined for Crossref purposes as "original content which is intended for formal publication, including content that has been submitted, but has not yet been accepted for publication."