When is it OK to use an ampersand (&) instead of the word "and"?
The ampersand (&) is a symbol for and. Unlike the percent or degree symbol, you generally shouldn't use the ampersand except in the most informal situations.
Some style guides allow ampersands as part of a formal company name (Smith & Wesson, Tiffany & Co.). Other style guides recommend spelling out the and in such cases. Most style guides recommend using the ampersand when the rest of the name is also an abbreviation (AT&T) and in common expressions (R&D). As you see here, there are no spaces on either side of the ampersand when it is used that way.
In common phrases, and can also be abbreviated using apostrophes for the missing letters: rock 'n' roll.
Get more tips like this in The Grammar Devotional: