Design today speaks fluently of care—empathy, inclusion, community—but rarely of justification. Design Ethics addresses this gap by offering a reproducible, institution-ready method of ethical reasoning that can be taught, audited, and applied across professional design practice. Drawing on the procedural transformation of biomedical ethics following the Belmont Report, Jeffrey W. Bulger develops a parallel framework for architecture, planning, and the built environment. Where professional codes—UIA, NCARB, AIA, ARB, RIBA, RAIC, and NSCA—define obligations but avoid adjudicating ethical trade-offs, Design Ethics supplies the missing structure for deliberation and justification. Bulger translates Principlism’s triad—Respect for Persons, Beneficence, and Justice—into design’s operative grammar: Duty, Consequence, and Fairness. These principles are operationalized through practical instruments—the Duty Statement, Consequences Ledger, Fairness Report, and Design Ethics Board—that convert moral intention into publicly defensible decision-making. Aligning ethics with the logic of the scientific method—hypothesis, evidence, review—Design Ethics reframes ethics as professional infrastructure, accountable to institutions and affected communities. Integrated appendices extend the method into procedures, governance, and pedagogy, ensuring ethical reasoning remains durable beyond individual judgment. Ethics becomes method.