The Inner Castle or the Book of Mansions is the masterpiece of Saint Teresa of Avila. It is one of the most important works of spirituality and the mystical experience of the West. The Carmelite Thérèse of Jesus, future saint Teresa of Avila, wrote this mystical work initially entitled, "Las Moradas" (meaning "Les Demeures"). It will finally be released under the title Castillo interior.

The image of the Castle refers to the soul that must go through successive stages to reach perfection. These stages correspond to the seven dwellings, in which the soul gradually perfects itself before reaching the ultimate, where God is. The prayer of recollection with the consideration of the person to whom one speaks, the asceticism, the prayer and the meditation are the gateways of the castle which allow to reach the ecstasy of pure Love, to the Divine Union.

Thérèse is canonized in 1622, her liturgical feast is fixed on October 15th. In the twentieth century, she was declared a doctor of the Catholic Church; she is the first woman to obtain this title.