This article explores the renovations of the ceremonial rooms of the Vatican Palace executed by Antonio da Sangallo the Younger under Pope Paul III Farnese (r. 1534-49). The focus of the investigation is the evolution of Sangallo's design for the Cappella Paolina. From the evidence it is clear that the various ceremonial and liturgical functions performed in the chapel defined the ultimate design and the strategic, yet problematic, location at the nexus of the papal palace and St. Peter's basilica. The Cappella Paolina replaced the medieval Capella parva and assumed its functions, which necessitated that the new chapel be built in an analogous form and site in order to maintain papal ceremonial continuity. A new look at documentary evidence provides a revised chronology for the construction of the main ceremonial spaces and a new sequencing and interpretation of the surviving drawings.