Chapter 5 deals with the most important subject area in administrative law; agency rulemaking. Emphasis is placed on the great importance of the rulemaking function, noting that over 90% of the public policies under which we live are made by our public administrators. This is due to the fact that our legislators have delegated broad lawmaking powers to public administrators because agency administrators have the expertise to promulgate regulatory policies to govern all sorts of (socio-)economic and political activities that require specialized knowledge—knowledge the legislators do not have. Substantial space is devoted to the democratic character of rulemaking and various rulemaking approaches, such as formal rulemaking, notice and comment rulemaking, and negotiated rulemaking. Significant attention is also given to considering the best method for promulgating public policies, rulemaking, or ordermaking. The chapter finishes with a famous case, Motor Vehicles Mfrs. Asso. v. State Farm, that makes clear that agencies cannot rescind rules unless they have good reason to do so rooted in science. Such prevents agencies from acting in an arbitrary and capricious manner so those regulated by agencies can depend upon consistent policy over time.