The business memorandum is essentially an “internal” business letter that does not go outside of an organization. (as opposed to letters, which do go to outsiders).
The “memo” as it is usually called, is the key internal communication tool in most businesses and institutions. In fact, the business memo is arguably the most important communications instrument in an organization.
Memoranda are used to: announce, inform, advise, quantify, delegate, direct, discipline, instruct, request and transmit. In short, if something needs to be communicated and/or recorded formally in an organization, it is done with a memo.
In many large organizations the corporate memorandum is the key “power instrument” when it comes to internal politics. Entire careers, and multi-million dollar programs, often hinge on the wording of a single memorandum.
Most large organizations have their own corporate format for their memos. The following is a recommended format for a generic internal business memorandum.
Business Memo Format

When reviewing this sample memo, please note that I have included a signature line at the bottom. Many organizations don’t require this signature line on a memo. I personally believe that a memo should have a signature on the bottom if it is to have maximum impact and credibility.
The above business memo format sample was copied directly from my business writing style guide Instant Business Letter Kit. That Kit contains almost 200 pages of business letter writing tips, techniques and information, including more than 125 real-life fully-formatted business letter templates that you can instantly download into your word processing program and work with as you please.
http://instantbusinessletterkit.com
In addition to the above format for “business memo”, you may also be interested in some of the other typical letter formats, depicted elsewhere on this site, that are often used for other business and personal situations:
Other Letter Formats