An overlay journal or overlay ejournal is a type of open access academic journal, almost always an online electronic journal (ejournal), that does not produce its own content, but selects from texts that are already freely available online. While many overlay journals derive their content from preprint servers, others, such as the Lund Medical Faculty Monthly, contain mainly papers published by commercial publishers, but with links to self-archived preprint or postprints when possible.
The editors of an overlay journal locate suitable material from open access repositories and public domain sources, read it, and evaluate its worth. This evaluation may take the form of the judgement of a single editor or editors, or a full peer review process.
Public validation of subsequently approved texts may take several forms. At its most formal, the editor may republish the article with explicit approval. Approval might take the form of an addition to the text or its metadata. Or the editor may simply link to the article, via the table of contents of the overlay journal. An alternative approach is to link to articles already published in various open access ejournals, but adding value by grouping scattered articles together as a single themed issue of the overlay journal. Such themed issues allow the focussed coverage of relatively obscure or newly emerging topics.