If for any reason you need to amend a previously filed tax return, you must use Form 1040X to correct the error or change in tax status.

This is the simplest IRS tax return form, and it can only be used by certain taxpayers meeting specific qualifications. Over the years, though, the one-page 1040EZ has become more and more complicated, and as a result more and more taxpayers are eligible to use it.

This is the "medium size" IRS tax return form, and it should be used by those taxpayers who are not eligible to use the Form 1040EZ short form. There are restrictions on who may use this form, and itemized deductions are not allowed.

If you send in a payment by check, you must also complete Form 1040-V and include it with your tax return. The IRS requests that you don't staple the check to your return, but simply enclose it in your envelope.