Co-branding strategies involve the collaboration between two or more brands in order to launch a new product co-named by these two brands. This paper aims to better understand the effectiveness of the co-branded product. The first contribution of this paper is to define effectiveness by distinguishing attitude (hedonic, utilitarian, and symbolic) from behavior (purchase intention and recommendation intention) towards the co-branded product. The second contribution is to propose a model where the relevancy/expectancy approach of congruence is used to explain the effect of moderate incongruence when concerning brand-alliances. Finally, the third contribution of this research is to highlight the two mediating effects of perceived innovativeness and credibility, depending on the level of congruence.