This chapter examines when and how mandatory rules should complement freedom of contract. It outlines four core justifications across consumer and B2B contexts: strengthening substantive autonomy where consent is illusory, correcting market failures, safeguarding fairness, and advancing distributive justice. It then identifies recurrent conditions that warrant mandatory rules, including unread standard form contracts, bounded rationality, information asymmetry and negative externalities, and significant power imbalances. On implementation, the chapter analyzes institutional choices among legislatures, courts, and administrative agencies; the rule–standard tradeoff; and design features such as positive versus negative framing, uni- versus bi-directional immutability, and in-contract disclosure of mandatory protections. It further classifies remedies for unenforceable terms (punitive, moderate, and minimally tolerable substitutes) and options for the remainder of the agreement (voiding, severance, or judicial adjustment). Ultimately, the chapter contends that carefully designed mandatory rules can make consent more meaningful while preserving the core values of contractual freedom.

Forthcoming in the Oxford Handbook of Regulatory Contract Law. The full paper is available on SSRN