What requires you to file a tax return?

To determine if you are required to file a federal income tax form, see Tables 1, 2, and 3 on pages 2, 3, and 4 of Publication 501:

State income tax requirements are different than federal. You should consult the instructions that come with your state tax forms or you might be able to find the information on your state tax department's web site.

Even if you are not REQUIRED to file, if you had tax taken out of your salary, pension, Social Security, or other payments, you should file in order to get a refund.