The paper highlights and discusses concepts and practices of national library digitization. Two conceptual models are suggested in order to help strengthen scholarly analyses of digitization practices within libraries: the distinction between quantitative and qualitative digitization, on the one hand, and the prism metaphor for understanding the nature of qualitative digitization, on the other. Qualitative digitization, understood as a document representational practice, is defined as a knowledge organization practice. These concepts and models are then put in relation to the issue of national libraries and institutional identity. By combining research within the fields of KO, digitization and institutional identity, the paper points to a way of addressing empirical issues in all three fields of research. Special focus is on the very definition of qualitative digitization as a KO practice and the practice of selecting and digitizing documents suitable for the development of institutional identity within libraries.