A stylistic analysis of the incised patterns executed on the shoulders of the pottery of five Central and Northern Plains village groups yields two broad pattern types. The configurations of these types and their variants in time and space conform to what is now known of the development of the five historic socio-linguistic groups considered: Pawnee, Arikara, Cheyenne, Crow, and Mandan-Hidatsa. The spread of a distinctive triangular pattern, the “Alternating Triangle,” from its inception along the eastern boundary of the Central Plains, provides a test of the hypothesis that incised Plains pottery shoulder patterns derive in large part from stimuli from Mississippian groups to the east. Subsequent history of the incised patterns is that of a strong collective tradition over-riding earlier patterns in the Northern Plains. This incised tradition is related to historic data on skin and robe painting and to the concept of a general art style of the area, as well as to fundamental problems in the field of art.