True Devotion to Mary is a treatise of what it means to have devotion to Our Lady. Montfort goes through the various aspects of this devotion explaining what is true devotion and outlining what is false devotion. The book also includes a series of meditations and prayers that assist in making a consecration to the Blessed Virgin Mary.

Montfort explains that devotion to Mary is not an optional devotion like any other devotion to the Saints. He boldly claims that devotion to Mary is necessary in becoming a living image of Christ in this world. He makes no distinction between devotion to Mary and devotion to Jesus. He invites those that are capable of understanding this devotion to embark on a journey of entering more deeply into the inner life of Jesus and Mary and by so doing to grow in holiness. (Summary by Michael Portelli)