The content of Digital Transformation (DT) as a factor of research library sustainability is revealed. In Part 1 of the study, the current status of transformation of modern society into the one based on information and knowledge, is discussed. The definitions of DT and its major attributes in respect of library development are provided. The definition of Sustainable Development (SD) is cited, along with 17 global Sustainable Development Goals (SDGs) to be achieved by 2030 approved by the UN General Assembly in 2015. In particular, the SDGs to be realized through introduction of modern digital technologies, are specified. Research libraries are expected to play an active part in this process. The activities of the IFLA Environment, Sustainability and Libraries (ENSULIB) Section are discussed. The ENSULIB special project – designing and maintaining the special page dealing with green and sustainable libraries on the IFLA website – The Green Library Website – is analyzed. The website is an example of organization of thematic e-space comprising various aspects of green and sustainable librarianship. The authors conclude on the two major related trends in librarianship. Trend One – orientation towards SD, creating green and sustainable libraries. Trend Two – successful digitalization and DT of libraries to facilitate the libraries enrollment into the green movement.