This article is an inquiry into the nature and roles of rulemaking and adjudication in shaping public policies in the American political system. Rulemaking and adjudication are compared in terms of policy formulation by administrative agencies. The political contexts of the two procedures are explored, with reference to the US Federal Communications Commission and to its counterpart in South Korea. Public policies shaped by the closed systems and administrative discretion of government agencies often have negative side effects that reach far beyond the interested parties immediately affected. The procedures of quasi-legislative rulemaking and quasi-judicial adjudication act as institutional safeguards. They oblige public agencies to follow due process when they are formulating public policies, thereby protecting the public from the abuse or misuse of administrative discretion. If the Korean government systematically institutionalises and operates such rulemaking and adjudication procedures in an effective way, Korean citizens and private companies may have formal or legal opportunities to express their opinions and appeal decisions adversely affecting their interests to a higher authority, including the judiciary. The congressional system may closely oversee the inner practices of policy formulation by administrative agencies, and the Korean President may effectively and impartially monitor the exercise of bureaucratic discretion in public areas of national importance