Updated October 8th, 2020.
⌘-I toggles italics on and off. This works almost everywhere on a Mac– Mail, Pages, Text Edit, you name it. Even Microsoft Word. Highlight some text, hit ⌘-I, and the text becomes italicized– unless it was already italicized. In that case, the italicizing is removed. It’s a toggle.
Microsoft was the most notable exception to this standard keyboard shortcut. Rather than using standard keyboard shortcuts that everyone already knew, early versions of Word used Command-Shift-I for italics in Word, along with Command-Shift-B for bold and Command-Shift-U for underline. Eventually Microsoft switched to the shortcuts everyone else uses– Command-I, Command-B, Command-U. Except the Command-Shift versions still work, so use them if you’d like.
Of course you can hit ⌘-I before typing something. If you do that, whatever you type after that is italicized, until you either hit ⌘-I again or click to type somewhere else.
This is very handy.
Did this article help you?
Maybe you'd like to contribute to theChristian Boyce coffee fund.

Want some some quick iPhone how-tos?
Visit me at iPhoneinaminute.com.
Looking for in-depth tutorials?
See my christianboyce.com website!

I used to be able to do this to get italics and underlining. Then, I had a problem with special characters — accented vowels, etc., so I set up Command plus the relevant letter to make those characters. I want to go back to having Command plus I give me italics and Command plus u give me underlining, but I don’t know how to turn off the accenting I set up with Command. I don’t remember where I set that up so that I can turn it off now. Please let me know if you have any suggestions. Thanks.
Hmmm. Third-party application maybe. Look in your Login Items (System Preferences/Users & Groups, then click your name, then click the Login Items button). See if something in there rings a bell. Typeit4me? Text Expander? Typinator? Maybe.