Legal and consumer psychology scholars have focused recent attention on source confusion, which is the likelihood that consumers will be confused regarding the company that is a product's source or sponsor. The authors evaluate two potential antecedents of source confusion: (1) consumer motivation and (2) a brand extension that has been undertaken by a competitor. There have been disagreements in the courts, the scholarly legal literature, and the consumer psychology literature concerning the nature and extent of the impact of these two variables on the likelihood of consumer confusion. Based on schema theory, the authors hypothesize that consumer motivation and brand extension will influence the likelihood of source confusion. An interaction between the two variables is proposed, with consumer motivation having an effect that is opposite to the effect typically identified in the literature and case law. The results of a controlled laboratory experiment support the theoretical predictions. © 2011 Wiley Periodicals, Inc.