The complex nature of large urban planning projects often results in delays or budget overruns. One of the causes is conflicts of interests between stakeholders. Recent planning failures in projects, due to limited public participation, sparked debates to increase citizen participation in formal planning procedures. This paper investigates how planning law supports public participation in large planning projects that cross municipal borders. The juridical analysis of German and Dutch codified law is based on four elements: literal content, institutional positioning, historical context, and teleological meaning of a legal text. The paper furthermore distinguishes four rationales for participation in planning: support,legitimization, improving plan quality, and education. The analysis shows that these rationales cannot be comprehensively regulated by codified law. Law can enhance the legitimate character of participation, but currently lacks the ability to organize support, improvement of planning, and education at the regional planning level.