Right now a valid driver's licence. Next year it will be a licence that meets the national Real ID standards. Valid state ID, or up to date passport.
Currently just the aforementioned items. After October 1, 2020 you will be required to provide either your passport, passport card or "Real ID. " https://www.dmv.pa.gov/REALID/Pages/default.aspx
Driver's licence/other state issued ID or passport and boarding pass
Drivers license or passport
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