This thesis addresses the significant issue of trademark counterfeiting on online marketplaces, with a specific focus on luxury goods. The distinctive characteristics of trademarks, rooted in consumer perception and the associated prestige, make luxury goods prime targets for counterfeiters. The anonymity and global reach of the internet facilitate the distribution of counterfeit goods, posing challenges for trademark owners to protect their intellectual property effectively. This paper investigates the extent to which current Swiss law provides civil liability for online marketplaces in cases of trademark counterfeiting. Through a comprehensive economic and legal analysis based on literature and case law, the supply and demand characteristics of counterfeit goods are explored and the effectiveness of the existing liability framework in mitigating this issue is assessed. The findings reveal that Swiss law predominantly relies on strict liability for negative actions, with considerable legal uncertainty surrounding reparatory actions. Although there is no specific duty of care mandated for platform providers under current Swiss trademark law, the enhanced protection for famous trademarks offers a viable defence for luxury brands, particularly through keyword blocking on internal search engines. The paper proposes a negligence-based liability framework, featuring a “Good Samaritan” clause, to encourage platforms to take reasonable steps against counterfeiting without the risk of over-removal of legitimate offers.