What's the Preferred Way to Write the Abbreviation for 'United States'?

(Getty Images)

As it happens, there's more than one preferred way to write the abbreviation for United States.

In general, newspaper style guides in the U.S. (in particular, the Associated Press Stylebook and The New York Times Manual of Style and Usage) recommend U.S. (periods, no space).* In headlines, however, it's US (no periods). And the abbreviated form of ​United States of America is USA (no periods). 

Scientific style guides say to omit periods in capitalized abbreviations, thus US and USA (no periods, no spaces).

The Chicago Manual of Style (2010) agrees—but allows for exceptions:

- Use no periods with abbreviations that appear in full capitals, whether two letters or more and even if lowercase letters appear within the abbreviation: VP, CEO, MA, MD, PhD, UK, US, NY, IL (but see the next rule).

- In publications using traditional state abbreviations, use periods to abbreviate United States and its states and territories: U.S., N.Y., Ill. Note, however, that Chicago recommends using the two-letter postal codes (and therefore US) wherever abbreviations are used.

My advice? Choose either U.S. or US and then stick with it.

*Note that British style guides recommend US (no periods, no space) in all cases: "Do not use full points in abbreviations, or spaces between initials, including those in proper names: US, mph, eg, 4am, Ibw, M&S, No 10, AN Wilson, WH Smith, etc." (Guardian Style, 2010). "Because American and British styles differ," notes Amy Einsohn, "CBE [Scientific Style and Format: The CE Manual for Authors, Editors, and Publishers] recommends eliminating periods in most abbreviations as the most efficient way to create an international style" (The Copyeditor's Handbook, 2007).