According to the National Rifle Association, some states have concealed carry weapons reciprocity agreements with other states, where each honors the other's concealed carry weapons permits. The website for USACarry has an interactive map that shows which states have reciprocity with each other.
USACarry says that in some cases one state accepts the concealed carry permit of a second state, but the second state does not accept the first state's concealed carry permit. According to ConcealedNation, state laws and reciprocity are subject to frequent change. USACarry includes up-to-date notes regarding changes to state reciprocity and also includes which states have exceptions to reciprocity statutes. Gun owners should seek legal counsel if there is any confusion about concealed carry weapons permit validity between different states.