The Handbook contains research results on the state of play of sustainable internationalisation in Higher Education Institutions, as well as important resources that can be used to embed environmental sustainability in internationalisation processes. The Green Erasmus project strived to improve the environmental sustainability of the Erasmus+ Programme and raise awareness across the European Higher Education sector about the importance of sustainable internationalisation. The project focused on developing an Educational Portal on Sustainable Internationalisation and carrying out comprehensive analysis of the environmental impact of Erasmus mobilities.