Mississippian chiefdoms in the Eastern United States (A.D. 1000--1450) exhibited a variety of sociopolitical organizations. This research investigates the social and political organizations of Mississippian chiefdoms by identifying the ideologies promoted by Mississippian leaders. A model is developed that describes social organization according to three dimensions of variation: Self-Orientation, Power Distribution, and Regional Interaction. Each organizational form encourages the adoption of certain kinds of ideologies, and each kind of ideology materializes as iconography with distinct characteristics. This model is applied to iconographic data from four Mississippian chiefdoms: Angel, Kincaid, Wickliffe, and Moundville. On the basis of non-iconographic data, a hypothesis is developed describing the expected sociopolitical organizations of the four sites relative to one another. On each of the three organizational dimensions, Angel should rank as the lowest, most horizontally organized site; Moundville should rank as the highest, most vertically organized site; and Kincaid and Wickliffe should rank in between, although their order relative to one another cannot be predicted. To test this hypothesis, observed characteristics of iconography are used to infer aspects of ideology. Because those aspects of ideology justify and rationalize the hypothesized sociopolitical organizations, the hypothesis is supported. Data for this analysis were collected from iconographic artifacts previously excavated from these four sites. Five iconographic variables were considered: medium type, symbolicity, individualization, theme standardization, and symmetry. Difference of proportions statistical tests were then performed for each variable, for each pair of sites. The results of these tests were combined to create multivariate ordinal rankings of all sites along each of the three dimensions. The multivariate rankings of the four sites generally agreed with the hypothesis. Two main conclusions can be drawn from the analysis. First, the hypothesis is correct. Angel was least hierarchically organized of the four sites, and Moundville the most hierarchical; Kincaid and Wickliffe ranked in between the others. Second, the model linking organization, ideology, and iconography is useful for investigating the sociopolitical organization of Mississippian chiefdoms.