Among the most knotty problems faced by investigators committed to interpretive practices in disciplines and fields such as sociocultural anthropology, jurisprudence, literary criticism, historiography, feminist studies, public administration, policy analysis, planning, educational research, and evaluation are deciding whether an interpretation is credible and truthful and whether one interpretation is better than another. After a brief introduction by Schwandt, in which he discusses the broad philosophical debate about the justifiability of interpretations, this chapter continues with Lincoln and Guba's argument for the way those committed to the interpretive practice of evaluation could profitably address the difficult problem of demonstrating the credibility of their interpretations. They describe two approaches to the justification of interpretations: (1) employing "trustworthiness" criteria (internal validity, external validity, reliability, and objectivity); and (2) employing "authenticity" criteria (fairness, ontological authentication, educative authentication, catalytic authentication, and tactical authenticity).