What is open access?

Open access means a research output can be read online for free, without a subscription. In gold open access the publisher makes the final version free; in green open access the author deposits a version in a repository or on a preprint server. Services such as Unpaywall and CORE find these free, legal copies from a DOI.

Many funders require open access, so a free version of recent research often exists somewhere.

Legal free copies are safer than shadow libraries, whose files can be altered.