Results of climate change, mostly caused by human activity, have stimulated the development of ecological thinking with the aim of preserving the planet. A library, in accordance with “IFLA’s statement on libraries and development”, is acknowledged as cultural and informational hub, thus the consideration of climate change made establishing green libraries possible. The green library is seen as a sustainable building within different sustainable practices, but the green library is also a concept of activities, services, collections and corpora prepared by the library for its users. The green library promotes eco-friendly user behavior, thus the libraries are focused on green literacy. The aim of this work is to show what libraries do as advocates of sustainable ideas and to display acts which are in compliance with the concept of sustainable development. Main part of the piece shows the creation of the green idea in library practices. The founding of Working Group for Green Libraries initiated the development of green library programs in Croatia and from that moment, in accordance with global trends, activities seeking to make ecology topics as available as possible to the users begin to take place, then the librarians connect them with local issues depending on the type of library. The final part of the work is focused on practices of Croatian libraries in regards to green literacy efforts by displaying library activities such as various projects, education courses and workshops.