Every year IRS audits are conducted in two ways. Each tax return is processed through a computer program called the Discriminate Information Function (DIF). The purpose of the DIF is to identify returns that have unusual deductions or where income does not match supporting documentation. The IRS will also randomly choose returns for audit or based on some criteria only the IRS knows. Some audits are conducted through the mail and you only have to send in additional documentation to support items on the return. But some audits are conducted in person. You will get a letter in the mail telling you that you are being audited and requesting you contact the IRS to make an appointment. It is important to properly prepare for the audit by assembling all of the records needed to support your tax return. The IRS will complete a detailed review of your bank statements, earnings statements and the documentation for most of the deductions. It is up to the auditing agent to decide what he or she wants to look at though agents have an audit guide they follow.