What is a pre-print?
A pre-print is the original draft version of an article as submitted to a journal, but it has not gone through a peer-reviewed process yet.
When can you upload?
The uploading of pre-prints is usually determined by the publisher of the journal an article has been submitted to.
The majority of publishers will highlight this in their Guidelines to Authors. Some will even supply authors with pre-print copies specifically to be uploaded onto an institutional repository.
The RoMEO Journals database can also be consulted to determine which publishers allow pre-prints to be uploaded. The RoMEO database aggregates and analyses open access policies of publishers from around the world and provides information on self-archiving permissions and author's rights.