Anatomy of green open access

Open access (OA) is free, unrestricted access to electronic versions of scholarly publications. For peerreviewed journal articles, there are two main routes to OA: publishing in OA journals (gold OA) or archiving of article copies or manuscripts at other web locations (green OA). This study focuses on summarizing and extending current knowledge about green OA. A synthesis of previous studies indicates that green OA coverage of all published journal articles is approximately 12%, with substantial disciplinary variation. Typically, green OA copies become available after considerable time delays, partly caused by publisherimposed embargo periods, and partly by author tendencies to archive manuscripts only periodically. Although green OA copies should ideally be archived in proper repositories, a large share is stored on home pages and similar locations, with no assurance of longterm preservation. Often such locations contain exact copies of published articles, which may infringe on the publisher's exclusive rights. The technical foundation for green OA uploading is becoming increasingly solid largely due to the rapid increase in the number of institutional repositories. The number of articles within the scope of OA mandates, which strongly influence the self-archival rate of articles, is nevertheless still low.