Proceedings of the National Academy of Sciences of the United States of America (often abbreviated PNAS or PNAS USA) is a peer-reviewed multidisciplinary scientific journal. It is the official journal of the National Academy of Sciences, published since 1915, and publishes original research, scientific reviews, commentaries, and letters. According to Journal Citation Reports, the journal has a 2022 impact factor of 9.4. PNAS is the second most cited scientific journal, with more than 1.9 million cumulative citations from 2008 to 2018. In the past, PNAS has been described variously as "prestigious", "sedate", "renowned" and "high impact". PNAS is a delayed open-access journal, with an embargo period of six months that can be bypassed for an author fee (hybrid open access). Since September 2017, open access articles are published under a Creative Commons license. Since January 2019, PNAS has been online-only, although print issues are available on demand. Source: Wikipedia (en)