This thesis examines the principal sources of legal uncertainty in the regulatory framework for online choice architecture (OCA) in EU law. It focuses on the EU Unfair Commercial Practices Directive 2005/29/EC, the EU Consumer Rights Directive 2011/83/EU and the EU Unfair Contract Terms Directive 93/13/EEC as horizontal instruments of EU consumer law, complemented by the EU Digital Services Act Regulation 2022/2065 (DSA). Online choice architecture describes the environment in which online users make decisions and inherently steers their decision-making. The current legislative framework for OCA that is designed and organized for commercial purposes is fragmented on multiple levels. On one side is the EU legislator’s tentative approach, mainly tinkering around the edges of traditional consumer law instruments that are ill-suited to address digital influence over choices, even when introducing a standalone prohibition of certain online choice architecture in the DSA. This approach has left considerable ambiguities. On the other side are recent consequential but equally ambiguous interpretative shifts of the normative framework of consumer law by the Court of Justice of the European Union. This has produced an uncertain regulatory regime in need of reform. This thesis establishes different forms of online choice architecture and the distinct ways they influence choices, leading to divergent legal assessments. It then analyzes applicable provisions of the UCPD, CRD, UCTD and the DSA to identify the respective and overarching sources of legal uncertainty, concluding with the overall need for further legislative intervention.