ABSTRACT The paper presents a methodological approach for assessing the personality of a dyad or a group, a concept that is not equivalent to the sum, or mean, of the individual scores. We illustrate how the logic of the multitrait multimethod approach, which is a familiar technique for establishing construct validity, can be extended to assess the construct of a relationship “personality.” The model, which we call the latent group model, provides a decomposition and comparison of individual-level and group-level variance in a given trait, and the individual-level and group-level covariance or correlation between two traits. The model is also extended to the assessment of stability of the individual and group level traits. Throughout the paper, we draw connections between related methods and show how the latent group model can be estimated through hierarchical linear modeling.