The fatal shooting of Philando Castile last year by a Minnesota police officer reinvigorated an old debate about how people who are licensed to carry a concealed weapon (CCW) should handle interactions with the cops. The officer, who was acquitted of manslaughter in June, panicked during a traffic stop after Castile, a CCW licensee, told him he was armed.

Some gun owners argue that disclosure is considerate and prudent, while others worry it will escalate a routine traffic stop into a tense, unpleasant, and possibly life-threatening encounter. But virtually everyone agrees it's important to know the relevant legal requirements, which vary from state to state.