It’s graduation season, and those of you who have just received doctorates have probably wondered how, exactly, to abbreviate the degree. And the heat of the moment is not really the right time to look this up (“Let me just put down my mortarboard for a sec and read the Manual, Mom…”). But if you have to add it in after your name to properly present yourself in a professional context, then it’s worth doing right. The expression, which technically stands for the New Latin term philosophiae doctor, is properly spelled “PhD,” not “Ph.D.” or “PhD.” (don’t retain the periods). Why? You’ll have to ask The Chicago Manual of Style 10.4 yourself—fruitlessly—for the logic, but the manual instructs us to leave off periods in abbreviations that end in a capital letter.