The abbreviated Latin terms e.g. and i.e. are often confused and used incorrectly. E.g. stands for exempli gratia, which means “for example.” I.e. stands for id est, which means “that is” or, put another way, “in other words.” The two abbreviations have distinct meanings and should not be used interchangeably:
Jeff and I are traveling to Minnesota to visit some of our old stomping grounds—e.g., our old apartment and the movie theater where we worked.
Because e.g. means “for example,” the apartment and the movie theater are just examples of some of the places we visited; we visited other places as well.
Jeff and I are traveling to Minnesota to visit some of our old stomping grounds—i.e., our old apartment and the movie theater where we worked.
Here, because i.e. means “that is,” the apartment and the movie theater are the only places we visited; mentioning them provides further explanation.
To borrow a “quick and dirty tip” from Grammar Girl, you can remember the difference between e.g. and i.e. by associating the abbreviations with their English meanings:
e.g. →for example
i.e. →that is, in other words
Although I’ve used italics in my discussion here for clarification, don’t italicize e.g. and i.e. in your writing. Yes, they are abbreviations for words in a foreign language, which usually are italicized, but they’ve become so standard in English that they no longer need to be. Do, however, put a period after each letter—they are abbreviations, after all—and always follow e.g. and i.e. with a comma.
Chicago Manual of Style, The. 15th ed. Chicago: The University of Chicago Press, 2003.
Fogarty, Mignon, Grammar Girl’s Quick and Dirty Tips for Better Writing. New York: Holt Paperbacks, 2008.