It depends. If you e-filed you don’t have to send in any forms in unless you was instructed to do so. However, there are some situations where you might have to mail something after e-filing, for example if your return contains Form 8453. If you completed a paper return, you would need to include copies of your W-2 and any forms that show income tax withheld. Also, make sure you sign your return because it will not be valid unless your signature is on it.