Abstract: Restatements interact with the common law in multiple ways. Restatements reflect the common law, but they also may do much more; for example, they may accelerate legal reform, and they may freeze the law in place. This chapter considers ways that Restatements can address a concern that Justice Cardozo emphasized: the need for a balance between certainty and flexibility. With that in mind, a central concern is the way that the common law operates as a complex system. The system of the common law is a hybrid of a spontaneous and a made order; it is also, potentially, a loosely connected system rather than the kind of deductive system that some formalists imagine. Taking these features into account, we argue that a key consideration in the drafting of Restatements should be the architecture of the common law, including its conceptual structure. Restatements can seek an “architectural fit,” and in doing so they can strike a workable balance between certainty and flexibility.