From the official US Federal Trade Commission site:
A recent amendment to the federal Fair Credit Reporting Act requires each of the nationwide consumer reporting companies – Equifax, Experian, and TransUnion – to provide you with a free copy of your credit report, at your request, once every 12 months. But there’s only one online source authorized to do so. That’s annualcreditreport.com. Beware of other sites that may look and sound similar.
Viewing your credit report is an important step to financial security. You should review your credit reports annually (at least) to correct and any errors. Also doing so can be a tool to help you spot identity theft. The credit report site also has a large frequently asked question section with answers to questions like: What is a credit score? How do I request a “fraud alert” be placed on my file? Should I order all my credit reports at one time or space them out over 12 months? (I would suggest spreading the requests out during the year myself).
Reposting, original is from last January.