Should i staple or paperclip W2's when filing taxes by mail?

[HelenaC]

I would staple the required forms where indicated on the front of your form 1040, 1040A or 1040-EZ. See 2017 Instruction 1040 - Internal Revenue Service. 

Most state returns have instructions on where and how to attach the required forms. Look up the state form instructions for the information.