In humans and animals, body posture is used in social and affective contexts to communicate social information, signal intentions, and prepare the individual for adaptive action. However, though stable individual differences in affect and social cognition are well studied, body posture continues to be typically studied in the context of state variation, and it remains unknown if trait-level differences in body posture exist and carry information about the individual. In our article, we show in a large sample (total N = 608 across five studies) that individual differences in body posture measured in a natural, baseline context are robustly associated with individual differences in personality. Through a series of studies, we characterize this relationship as reflecting individual differences in postural dominance and submission, which are associated with attitudes toward competition, power, and social hierarchy. We also validate our measure of natural posture by correlating it with physiological data from relevant musculature and showing its stability over a 1-month interval. Our work suggests that postural signaling of social rank occurs not just in brief displays in social contexts but exists as a stable individual trait with consequences for socioaffective processing. (PsycInfo Database Record (c) 2024 APA, all rights reserved).