Branding studies, especially those focusing on brand extension, have often centered on establishing the relationship between consumer evaluation and the match between a product concept and the brand (concept congruity). This study introduces an additional type of congruity that arises in the evaluation of co-branded products, the congruity between brand partners (between-partner congruity). Between-partner congruity has not previously been explicitly considered in the co-branding literature, but is potentially an important influence on consumer perceptions of a brand partnership. Thus, this study represents an initial attempt to understand how the level of between-partner congruity will affect consumer response to cobranded products. Several findings in the marketing literature have suggested that when respondents have the motivation to resolve incongruity, the relationship between congruity level and evaluation is nonmonotonic. In other words, moderately incongruent concepts are preferred to congruent or highly incongruent concepts to form an “inverted-U” data function. Yet, when motivation to process is low, evaluation becomes less favorable in a linear fashion as incongruity increases. This study examines whether these findings can be extended to co-branding. When concept congruity is controlled across brand pairs, the nonmonotonic relationship between between-partner congruity level and product evaluation is observed when consumers are encouraged to elaborate on the rationale for the partnership (high involvement). However, when consumers attend to the global similarity of the partners (low involvement), product evaluation becomes less favorable as between-partner incongruity increases. © 2007 Wiley Periodicals, Inc.