A DOI, or Digital Object Identifier, is a unique and persistent identifier used to identify various objects, such as journal articles, research reports, data sets, and official publications. It is a string of numbers, letters, and symbols assigned to an article or document to provide it with a permanent web address (URL) . DOIs are standardized by the International Organization for Standardization (ISO) and are an implementation of the Handle System. They are widely used in academic, professional, and government information. DOIs are important in academic citation because they are more permanent than URLs, ensuring that readers can reliably locate the source. A DOI is assigned by a publisher when an article is published and becomes accessible online. It is usually printed with the article itself, usually on the first page somewhere: below the title or in the header or footer. If the DOI isnt included in the article, it can be looked up on the website CrossRef.org. A DOI can appear as either an alphanumeric string of digits or as a webpage URL. APA style recommends including the DOI at the end of a reference, starting with https://doi.org/.