A DOI (Digital Object Identifier) is a string of numbers and/or letters that uniquely identifies a book or article. Unlike a URL, the DOI of an item does not change when that item is moved from one location to another on the Internet.
Example:
doi:87.1678/16076320414622005
There are a number of ways to find the DOI of an item:
1) Look on the first page of an article.
2) If you have accessed the article through a database, check the bibliographic record.
3) Go to CrossRef and search by the title of the item and the last name of the author.
4) Do a Google search for “title of the item” AND “doi”. This works particularly well for books.
Whenever possible, copy and paste DOIs rather than attempting to type them out, since accuracy is very important.