Since 1959—when she first appeared, at age eighteen, at the Newport Folk Festival, singing alongside the banjo player and guitarist Bob Gibson—Joan Baez has been electrifying eager crowds with her elegance and ferocity. Baez was central to both the folk revival and the civil-rights movement of the nineteen-sixties; her protest songs, delivered in a vivid, warbly soprano, felt both defiant and gently maternal. (Baez’s stunning 1963 performance of the century-old gospel song “We Shall Overcome,” at the March on Washington for Jobs and Freedom, remains one of the crucial musical artifacts of the era.)