"Diary of Saint Faustina Kowalska" is a spiritual journal written by Saint Faustina Kowalska, a Polish nun and mystic. The diary documents her experiences and visions of Jesus Christ, focusing on themes of divine mercy, love, and the importance of trust in God. It serves as a guide for spiritual growth and understanding of God's mercy. The diary is divided into several sections, each containing reflections, prayers, and revelations. It played a significant role in the promotion of the Divine Mercy devotion, which emphasizes God's forgiveness and compassion. The work has inspired many believers and is considered a key text in modern Catholic spirituality.