Evaluative conditioning (EC) is a key effect in attitude formation, leading to changes in the liking of neutral attitude objects due to their pairing with positive or negative stimuli. Despite EC's significance, current theories and most empirical findings are limited to stimulus pairings with a single affective stimulus at a time. In contrast, social environments often involve more complex combinations of affective stimuli. In this article, we introduce a novel framework grounded in information integration research to understand how conditioned attitudes develop in the presence of multiple affective stimuli. Through 10 experiments with different designs, measures, materials, and pairing procedures, we find that individuals' conditioned attitudes follow the average valence of all affective stimuli present with a stronger weighting of negative stimuli. This weighted averaging rule bears two implications for EC in more complex stimulus combinations. First, EC effects are nonmonotonous, such that additional stimuli of the same valence do not produce incremental EC effects. Second, EC effects are interdependent, such that the impact of one stimulus is weakest when accompanied by another negative stimulus and strongest when no other affective stimulus is present. We examine different cognitive processes underlying this weighted averaging rule, including potential differences in pairing memory or changes in the affective stimuli's valence when other stimuli are present. Our findings present a novel theoretical perspective on EC and offer valuable insights into attitude change from stimulus co-occurrences in stimulus-rich environments. (PsycInfo Database Record (c) 2024 APA, all rights reserved).