There are two main, non-exclusive ways of making publications and data Open : through self-archiving in repositories or through publishing in Open Access journals .
Publishing in an Open Access Journal : you can find a list of reliable Open Access journals in the DOAJ. If the publisher asks for an author fee (also: ‘article processing charge’ or APC), you can declare this an eligible cost in your project budget. Some Open Access Journals offer you the option of archiving the underlying data of an article you submit as well, and there are even journals who only publish datasets and their metadata.
By self-archiving their work in digital archives or repositories (‘depositing’), researchers can make their publication or data Open Access, even if the final published version of their work is not. This is possible even if you have assigned the copyright to your publisher (although the assignment of your rights is often negotiable when you ask your publisher about it). Some repositories only accept publications, but in other repositories you can also deposit datasets, whether they're connected with a publication or not.
Open Access is compatible with copyright, peer review, preservation, prestige, quality, career-advancement, indexing, and other features and supportive services associated with conventional scholarly literature.
In its Open Access policy for Horizon 2020, the European Commission explicitly asks to deposit the work in a repository and make it Open Access (after an embargo if necessary) – regardless of whether it has been published in an Open Access Journal or not.
A novelty in Horizon 2020 is the Open Research Data Pilot which aims to improve and maximize access to and re-use of research data generated by projects. It will be monitored with a view to developing the European Commission policy on open research data in future Framework Programmes.