The twentieth century witnessed declining interest in architectural proportioning systems, which were virtually eclipsed by technical, social and fiscal agendas. Louis Kahn is a seminal architect, whose most acclaimed building, the Kimbell Art Museum (1966–72), represents a compelling case-study in the use proportions by twentieth-century architects. In spite of a raft of peculiarly modern restrictions (both technological and programmatic), Kahn appears – despite his espoused ambivalence concerning proportion – to have intentionally produced a building with an array of approximate geometrical as well as precise harmonic proportions. This two-part paper presents the findings of a multifaceted research project that examined the Kimbell’s proportions from numerous standpoints. Part 1 presents a textural analysis of Kahn’s statements regarding proportion, as well as the findings of an archival study of correspondence between the architect and his client and consultants. Part 2 presents a prima facie geometrical analysis of the construction drawings for the project. The division into parts reflects an apparent discrepancy between Kahn’s buildings and what he had to say about them.