Nonreciprocal States
Two of Pennsylvania's neighboring states do not offer income tax reciprocity: Delaware and New York. This means, for example, a Pennsylvania resident working in one of those states must file a return in that state, pay the tax, and then take a credit on his or her Pennsylvania return.
If you live in Delaware or New York and work in Pennsylvania, your resident credit is limited to the lesser of the Pennsylvania tax you paid on the compensation earned in Pennsylvania or the resident state tax on the compensation.
If you live in Pennsylvania and work in one of the two nonreciprocal states, the Pennsylvania credit is limited to the lesser of the tax you paid to the nonresident state or the Pennsylvania tax due on the compensation that was taxed in the nonresident state.