What is this about?
Self-plagiarism is the practice of reusing significant parts of one’s own publication in another publication. Self-plagiarism is also known as duplicate (or multiple) publishing. Keep in mind that self-plagiarism is different from duplicate submission. 
- Thurman RH, Chervenak FA, McCullough LB, Halwani S, Farine D. Self-plagiarism: a misnomer. Am J Obstet Gynecol. 2016;214(1):91-3.
Why is this important?
For whom is this important?
What are the best practices?
Different fields take different stances in regard to self-plagiarism. For example, legal research has a lot more tolerance for reuse of one's work than biomedical science. In 1969, the scientific journal the “New England Journal of Medicine” announced they would no longer publish already published work. This is called Ingelfinger rule and became a norm for high quality scientific journals. Because of the rise of preprint servers (such as arXiv), journals now tend to loosen that policy. Secondary publications are a different issue, as they clearly state that work has been previously published. They are produced with a goal of reaching a bigger (and sometimes different) audience, often through translations to different languages.
Keep in mind that a lot of scientific journals use computer software to check if your text is similar to anything already published. The majority of software works through screening available online databases for similarities. 
- Altman LK. The Ingelfinger rule, embargoes, and journal peer review--Part 1. Lancet. 1996;347(9012):1382-6.
- Errami M, Sun Z, Long TC, George AC, Garner HR. Deja vu: a database of highly similar citations in the scientific literature. Nucleic Acids Res. 2009;37(Database issue
The Embassy Editorial team, Iris Lechner, Natalie Evans, Vassilis Markakis, Marin Vidak contributed to this theme. Latest contribution was Mar 27, 2021