ABSTRACT The internal-external model, originally published in Notes on Structural Integration, titled “Towards a Structural Logic,” in 1986 by Jan H. Sultan, is a foundational understanding of the nature of the human structure. Sultan has written a second edition of this model, informed by more than fifty years of practice and teaching. He describes the inspiration for and the history of the internal-external model and the value of the structural types – congruent internal, congruent external, and incongruentmixed types. The internal-external model is a structural language that was early to identify lines of force transmission. It is a structural description of the inherited direction of growth and adaptations visible in the fascial network.