Marketers cultivate brand relatedness in their brand portfolios to increase marketing efficiency through positive spillover of brand equity. However, creating linkages between brands may also make them vulnerable to negative spillover. This research investigates the structure of relatedness in a brand portfolio to understand the nature of spillover effects. The results of two experiments show that the magnitude of spillover between brands is a function of not only the strength of brand associations but also their directionality. The results also show that the directional strength of association is influenced by the number and salience of associations linked to each brand. The authors draw implications for a theoretical understanding of spillover effects in marketing, as well as for the management of brand portfolios.