The authors examine the growing and pervasive phenomenon of brand alliances as they affect consumers’ brand attitudes. The results of the main study (n = 350) and two replication studies (n = 150, n = 210) together demonstrate that (1) consumer attitudes toward the brand alliance influence subsequent impressions of each partner's brand (i.e., “spillover” effects), (2) brand familiarity moderates the strength of relations between constructs in a manner consistent with information integration and attitude accessibility theories, and (3) each partner brand is not necessarily affected equally by its participation in a particular alliance. These results represent a first, necessary step in understanding why and how a brand could be affected by “the company it keeps” in its brand alliance relationships.