There are three major credit-reporting agencies in the United States, Equifax, Experian, and TransUnion, and each one keeps a detailed record of your credit history. They are all storehouses of information, places where your creditors send details about your payment histories, current balances, credit limits, and personal information.

Credit-reporting agencies also receive reports about you from collection agencies, the court system, and other sources of public records. If there's a negative report floating around about your credit history, always assume it will make its way to at least one of the reporting agencies.

Each agency operates independently of the others, so records sometimes differ. Maybe a creditor didn't submit details about an account to all three, or perhaps a mistake occurred during the transfer of data. Each of the agencies handles hundreds of thousands of entries a day, so mistakes are common. It isn't unusual for the records of the three agencies to reflect a different set of “facts” about you and your credit history.