When should I use an ampersands(&)?

Only under the following circumstances:
-in certain company names, e.g. Smith & Jones Consulting.
-if space is very limited, e.g. in a table with a lot of text.
-when artistic considerations dictate, e.g. a logo.
-In MLA or APA citations the ampersand is used when citing sources in text such as (Jones & Jones, 2005). In the list of references, an ampersand precedes the last author's name when there is more than one author.

Do not use an ampersand in general writing simply to abbreviate the word "and". For example, we write:

We need to reorder toner cartridges and paper.

not:

We need to reorder toner cartridges & paper.

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