Chapter 4 investigates the foundation and early development of the Congregation of the Mission, a congregation of secular missionaries dedicated to evangelizing the rural poor (their mission) through the completion of formal missions in their parishes. Soon to be known as the Lazarists, the Congregation was endowed by patrons Philippe-Emmanuel and Marguerite de Gondi in 1625. The chapter explains how, in charting its course thereafter, de Paul was forced to confront pressing questions about the character, functioning, and durability of his new mission institute. It analyses his answers to these through a composite investigation of the three milestones of the Congregation’s early formation process: its initial foundation in 1625, the issuance of papal approval in 1633, and the controversial acquisition of the priory of Saint-Lazare in Paris in 1632.