<p>Nonprofit organizations (NPOs) have a moral obligation to act in the public interest and are thus expected to lead by example in transparency. Yet, by focusing on the benefits that NPOs derive from being transparent (i.e., the instrumental approach), prior literature has tended to neglect the view of transparency as a moral responsibility regardless of the associated benefits (i.e., the normative approach). We suggest that embracing a normative approach may enable a more comprehensive conceptualization and operationalization of NPO transparency. Based on a systematic literature review, this study conceptualizes NPO transparency as a three-dimensional construct, comprising completeness, accessibility, and inferability. Such conceptualization is then translated into an extensive transparency index that NPOs, with sufficient staff and resources, can use to monitor their practices. Finally, we assess the appropriateness of the conceptualization and the index through a content analysis of 432 NPO websites in Belgium. By highlighting inferability as an important but understudied dimension, we contribute to a more comprehensive normative understanding of NPO transparency.</p>