As long as you can be sure your readers will understand them, use common abbreviations such as PBS, NASA, DNA, and CIA. If an abbreviation may be unfamiliar, however, spell out the full term the first time you use it, and give the abbreviation in parentheses. After that, you can use the abbreviation by itself.

The Comprehensive Test Ban (CTB) Treaty was first proposed in the 1950s. For those nations signing it, the CTB would bring to a halt all nuclear weapons testing.