The main focus of the open access movement is "peer reviewed research literature." Historically, this has centered mainly on print-based academic journals. Whereas conventional (non-open access) journals cover publishing costs through access tolls such as subscriptions, site licenses or pay-per-view charges, open-access journals are characterised by funding models which do not require the reader to pay to read the journal's contents or they rely on public funding. Open access can be applied to all forms of published research output, including peer-reviewed and non peer-reviewed academic journal articles, conference papers, theses, book chapters, monographs, and images.