The Collected Letters of St. Teresa of Avila is a multi-volume collection providing a candid, "behind-the-scenes" look at the life and personality of the 16th-century Spanish mystic and Doctor of the Church. Unlike her formal spiritual treatises—such as The Interior Castle or The Way of Perfection, which were written with an eye toward ecclesiastical censors—her personal correspondence reveals an unvarnished and colloquial side of the saint.