The authors analyse, from a direct taxation perspective, the legal and operational aspects of the liabilities imposed on digital platforms to secure the collection of their sellers’ taxes. In particular, they focus on regimes that designate digital platforms as withholding agents or third parties jointly and severally liable for the payment of their sellers’ taxes. By looking at the regimes currently in force in four different countries (i.e. Belgium, Italy, Mexico and Uruguay) and using them as case studies, the authors make an in-depth comparative analysis of the withholding tax obligations imposed on digital platforms. Section 2.1. describes different approaches for establishing third-party liability for the payment of taxes in order to place those foreseen for digital platforms into this broader framework. Sections 3. and 4. provide a brief overview of tax regimes in the surveyed jurisdictions and a comparative analysis also in light of a comprehensive literature review. Section 5. addresses the imposition of withholding tax obligations on digital platforms and the aforementioned national regimes from a tax policy, fundamental rights and general legal/tax principles perspective. Section 6. provides a conclusion.