Q. Hi, I was wondering if you could clarify whether a DOI is required for citations of print sources when one is available.
A. According to CMOS 13.14, authors don’t need to record DOIs for print resources “unless their publisher or discipline requires it.” And because most readers will assume that a DOI in a citation means you’re referring to something online, it’s generally best not to include one for a work you consulted in print unless you’ve also consulted the online version. (It’s unlikely that a source that’s available only in print will have a DOI.)