A number of answers u2023 including one from a supposed IRS employee u2023 say not to physically attach them, but just to include the W-2 in the envelope.In fact, the 1040 instructions say to u201cattachu201d the W-2 to the front of the return, and the Form 1040 itself u2014around midway down the left-hand side u2023 says to u201cattachu201d Form W-2 here; throwing it in the envelope is not u201cattaching.u201d Anything but a staple risks having the forms become separated, just like connecting the multiple pages of the return, scheduled, etc.