The Green road – the author publishes in traditional journals and deposits his/her work in an open archive, as long as the publisher’s policy allows:

• Self archiving
• The archiving of a specific version of the article (e.g. pre-print, post-print, etc.)
• No embargo period before the work can be disseminated as Open Access

Self-archiving is allowed by most of the publishers. However, it is always recommended to check which version of the work is permitted for self-archiving.

Usually, the deposit is allowed to:

• preprint - the version of the work before the peer review;
• postprint - (aka Author's Accepted Manuscript - AAM) the final version of the work after peer review without the editorial layout;
• Version of Record (VoR) - the published version of the work with the editorial layout.

An embargo period may be requested by the publisher before allowing the deposit of the work in an open archive. The embargo begins the same day the article is published online in its definitive and citable version and is applied to the allowed version only (e.g. post-print).

The deposit of the VoR is allowed only if the article is published in a OA native journal or after the payment of an APC - Article Processing Charge.

An APC is a fee charged to the authors to publish Open Access either in OA native journals or in journals upon subscriptions proposing Open Access options (Hybrid Journals).

This fee may be paid by the authors themselves, by their institutions, or by their funders. Please notice that it is not the same fee as the one charged for additional pages or for pictures and colors.

The costs for Open Access may vary between publishers and journals. The EU consider them as eligible for reimbursement. They may be calculated in the project budget and declared in the Grant Agreement.

The Gold and Red roads – in both cases the author retains the copyright, as specific licenses regulate the use and the reuse of the scientific production by the reader (e.g. Creative Commons Licenses):

• Gold - the authors publish the article upon payment in peer-reviewed Open Access journals, accessible without subscription. Traditional publishers (e.g. Elsevier, Wiley, Springer, etc.) provide an “Open Choice” (e.g. Springer) for the payment of single articles through an Article Processing Charge (APC). 
• Red - the authors publish in “hybrid” journals upon payment, even though a subscription fee has been paid by their institutions.

The Diamond (or Platinum) road - is a fully OA publishing model. Diamond publications are usually financed and managed by Universities and Research Bodies through owned Academic Presses. They cope with the whole publishing cycle, from submission to peer review until publication. The scientific products are published online at free access. Their reuse for commercial purposes is not allowed. In addition, since March 2021 the platform Open Research Europe (ORE) has made available by the European Commission, which covers all publication costs. Another example of Diamond OA is SciPost, a publishing platform financed through the donations of the organizations that exploit its editorial services, with no additional costs either for authors or for readers.

If the publisher does not allow the immediate self-archive or the embargo period is longer than the period admitted by the funder, the author may opt for the Gold road and pay APC costs, for the Diamond road, or make reference to other useful tools and resources for Open Access.