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.
DOI codes are more stable than links, so if you have the option to use a DOI, do it.
For more information, see the APA guide to DOIs, or Wikipedia's entry for DOI.
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.
