E.g. vs. i.e.

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Although commonly confused and misused in colloquial English, e.g. (exempli gratia) and i.e. (id est), both from Latin, are not equivalents.

Exempli gratia, means "for example", and is used before giving examples of something ("I have lots of favorite colors, e.g., blue, green, and hot pink"). The latter, id est, means "that is", and is used before clarifying the meaning of something, when elaborating, specifying, or explaining rather than when giving examples ("I have lots of favorite colors, i.e., I can't decide on just one").

American style guides tend to recommend that "e.g." and "i.e." should generally be followed by a comma, just as "for example" and "that is" would be, while UK style tends to omit the comma.