Consumer researchers have conceptualized brand name dilution in terms of the potentially damaging effects that a company's own brand extensions can have on beliefs and attitudes toward parent brands. A different form of dilution, trademark dilution, can also occur through the unauthorized use of a mark (e.g., brand, logo) by an entity other than its owner. With passage of the Federal Trademark Dilution Act of 1995, an increasing number of trademark dilution cases are being litigated. A recurring issue in these cases has been how to measure trademark dilution. The authors review the concept of trademark dilution and explore how recognition and recall-based methods can be used for empirically assessing trademark dilution. The authors also investigate the impact of brand familiarity and product category similarity on the extent of trademark dilution and discuss implications, limitations, and areas for further research.