In this chapter, we argue that increasing policy complexity will contribute to a divergence of political debates. This divergence takes the form of a growing gap with respect to the handling of policy substance between two contexts of political debate: political debates that take place within epistemic communities and expert arenas, and political debates that take place in the public sphere. While political debates in the expert arena and political debates in the public arena are never completely congruent, their overlap decreases with increasing policy accumulation. As policy accumulation makes policy mixes larger and increasingly complex, the substance of public policy becomes less suitable for debate in the public arena and will become increasingly marginalized in public debates. Consequently, a growing level of policy-inherent complexity threatens to lead to a growing disconnect between public and expert arenas regarding the role of policy substance. This way, policy accumulation challenges the quality of policy debates, which constitute an important component of the input legitimacy of democratic political systems.