Acronyms and initialisms

What's the difference?
Both acronyms and initialisms are groups of letters that stand for a group of words. The distinction has to do with the way they are pronounced: True acronyms are pronounced as words (ERIC, JAAL, and UNESCO are good examples). Properly speaking, groups of letters that are pronounced separately (e.g., IRA, DNA, FBI) are initialisms. In common usage the distinction is ignored, and all such letter groups are referred to as acronyms. References to acronyms in this guide hold true for initialisms, as well.

acronyms, general rules

1. In most cases, spell out the word in full the first time it appears in an author’s work, and follow the full spelling with the acronym in parentheses. (If the acronym is better known than the full form, use the acronym first and follow with the full spelling in parentheses.) Thereafter, use the acronym only. (In edited books, spell out the word the first time it appears in each chapter.)
2. As a general rule, do not use an acronym unless it will be used again in the written piece (in the case of a short work, used at least one more time; in the case of a longer work, used several times). The advantage of using the acronym is lost if the reader has to spend a lot of time hunting down its meaning.
3. More obscure acronyms and abbreviations are listed in M.R. Bonk, ed., Acronyms, Initialisms, & Abbreviations Dictionary. (1997). Detroit, MI: Gale Research. Acronyms and abbreviations from many fields may also be found on The World Wide Web Acronym and Abbreviation Server.
4. Because of its politically charged connotations overseas, avoid using "the IRA" to refer to the International Reading Association on items that will reach an international audience. Spell out the full name, refer to “the Association,” or rephrase as necessary.  Use of "IRA" in running text is acceptable after the organization's full name has been spelled out and where an acronym is appropriate.
5. Acronyms are acceptable in headings if they have already been spelled out prior to the heading and can be used on a case-by-case basis if not spelled out prior to heading (with this exception noted on style sheet).
6. Acronym rules should be followed for front matter of books and abstracts of journals and for book or journal text. That is, for an acronym to appear in an abstract or front matter, it should appear at least one additional time in the abstract or front matter. First mention of the acronym in subsequent text should be spelled out.

*also, Arizona Reading Association; Arkansas Reading Association; Austrian Reading Association. (Use the acronym only when the context makes clear which organization is meant.)