A DOI (Digital Object Identifier) is a unique code that identifies an online publication such as a journal article. It has the format doi:10.0000/000. DOIs are assigned by the International DOI Foundation. Some citation styles, such as APA, recommend the use of DOIs in citations.
If you have a DOI, PubMed ID (PMID), or ISBN number, click on the magic wand icon from the Zotero toolbar and enter the number into the pop up window that appears at the top of your browser.