Theoretical, regulative and organizational foundations for developing e-libraries are discussed along with the experience of their operation in educational systems in Russia and worldwide. The author defines the digital (electronic) library of an educational institution as the integrated organizational, software and technological tools to support educational activities, computerize key library and information processes, integrated at the level of user data with library and information services within the e-libraries and public libraries, digital educational resources and platforms. When building the model of digital (electronic) library, educational organizations are recommended to apply service-based approach so to structurize the list of services of information acquisition, processing, storage, representation and delivery to library users, e. g. students, pedagogues, parents and administrators. The minimum requirements, including these used in the related information systems, to data within the service-based model are determined; the repertory of analytical digital services for assessing, forecasting and modelling of educational activities, is suggested. These approaches are efficient in digital transformation of libraries and building of digital (electronic) libraries within the structure of educational environment.