The Letters of St. Vincent de Paul is a compilation of authentic correspondence by Saint Vincent de Paul (1581–1660), a French priest known as the "Father of the Poor" and founder of the Congregation of the Mission (Lazarites) and the Daughters of Charity.

These letters showcase Vincent's humanistic and spiritual side. They include spiritual advice, practical guidance on managing charitable works, leadership, and daily interactions with various levels of society, from nobles to poor peasants. They emphasize practical service to the poor as an expression of love for God. Vincent often emphasized the phrase, "Love God with your hands until you are exhausted and with the sweat pouring down your face!" Many letters, addressed to Sister Louise de Marillac or members of the Congregation of the Mission, offer advice on humility, meekness, simplicity, and submission to Divine Providence (procredence). These letters were written in 17th-century France, a time of social turmoil and war, during which Vincent organized aid for war-affected areas, orphans, and the sick. This correspondence is a key source for understanding Vincentian spirituality, which combines contemplation (prayer) and action (active service). Taken together, this book provides a firsthand account of how Vincent directed his work to serving "Christ in the poor."