The abbreviation e.g.—short for the Latin phrase exempli gratia—means for example. It is different from i.e.—short for the Latin id est—which means that is, namely, or in other words. The two are sometimes mixed up, but other than being abbreviations of Latin phrases, they share no common ground.
E.g. is easy to remember because both it and example start with e. With i.e., just remember that it and that is are both two syllables, or make a mental connection between i.e. and the two-letter i words is and in in that is and in other words.
I.e. and e.g. are lowercase when they come in the middle of a sentence. Most American style guides recommend following e.g. and i.e. with a comma and including the periods after each letter, and this is usually borne out in edited American books and publications. Outside North America, the periods and the comma are often omitted.
There is no need to italicize e.g. and i.e. in normal use (we italicize them in this post because we’re discussing them, not using them). English speakers typically italicize words and phrases from foreign languages when they are new to English, but i.e. and e.g. have been in English for hundreds of years, so they now go unitalicized.
It’s early, and factors beyond anyone’s control (e.g. the euro, Iran) could impact the race. [Washington Post]
The Harvard report compared “professional” reviewers (ie those working for newspapers and magazines) with their new competition. [Guardian]
Prohibition of illegal substances (e.g. LSD or MDMA) has also prevented very important clinical research from continuing. [Sydney Morning Herald]
In 2005, America had the lowest personal savings rate since 1933. In fact it was outright negative — i.e., consumers spent more money than they made. [Chicago Tribune]
[T]he announcement … was so intoxicating to the world’s sci-fi geeks (e.g. me) that they’ve been gearing themselves up for a work of genius. [Independent]
The bulk – ie, about $3b – of new spending priorities announced today are reallocations of money from other uses. [Stuff.co.nz]