This is the first of two articles on the problem. The theoretical significance of the article lies in the demonstration of the potential of library user digital profiles (DP). The author examines the following problem components: a) user DP structure with specifying the layers – subject, object, domain, communications, and b) layer function – identification, clusterization, filtration, and collaboration. For each layer, the dominant factors are identified that enable to model, structure and use DPs for proactive meeting of library users’ information demands. The practical value of the study lies in the DP development and application for services personalization: proactive building awareness of new acquisitions, digital user support and curation, support of research projects; reconciling library collection and the demands of core user groups (collection structure enhancement, changing of the policy of acquisitions, cataloguing, and library services promotion); need-demand interdependence through using DP information, which makes acquisitions and services more efficient; and accommodation of library activities with local community’s plans and expectations.