The United Nations Secretary-General’s Global Education First Initiative (GEFI) has established education as a means to ‘foster global citizenship’ – one of its three priority areas. To support this, UNESCO organized two landmark meetings on GCE in 2013. This publication aims to define the parameters of GCE by using the collective expertise, experience and wisdom of those participants who gathered at these landmark events, and to plan for future action in line with emerging thinking and other ongoing work. The review establishes that GCE has a critical role to play in equipping learners with competencies to deal with the dynamic and interdependent world of the twenty-first century. While GCE has been applied in different ways in different contexts, regions and communities, it has a number of common elements, which include fostering in learners. In formal settings, GCE can be delivered as an integral part of an existing subject (such as civic or citizenship education, social studies, environmental studies, geography or culture), or as an independent subject area. Integrated models appear to be more common. Some less traditional, but at least as effective, pathways for GCE have included the following: the use of information and communication technologies and social media, sport competitions and the use of art and music, and youth-led initiatives employing a wide variety of approaches. Both traditional and new horizons for GCE are profiled in this review. This publication also explores a number of enabling conditions for the promotion and implementation of GCE. These include: the existence of an open environment for universal values, the implementation of transformative pedagogy and support for youth-led initiatives. The review acknowledges that there are a number of ongoing tensions with the concepts of global citizenship and global citizenship education. While these tensions vary, they all point to the fundamental question of how to promote universality (e.g. common and collective identity, interest, participation, duty), while respecting singularity (e.g. individual rights, self-improvement). Some ways forward to resolve these tensions are suggested, whilst maintaining that challenges around theoretical elements of GCE should not undermine its practice. The processes documented in this publication have strengthened partnerships, built coalitions and contributed to improving the evidence base on the theory and practice of global citizenship education. While there are tasks that remain, this foundation bodes well for improving the enabling conditions and the practices highlighted in this review. By preparing learners to fulfil their potential in an increasingly globalized world, we are promoting transformed societies that are also better equipped to deal with the twenty-first century challenges and to seize twenty-first century opportunities.