A Teacher's Handbook on Global Citizenship Education in the Post-primary Classroom is written by teachers for teachers. It seeks to support those new to the profession, as well as those who are already experienced in post-primary school and further education settings. It is designed to sustain these professionals in their important - relational and pedagogical - work with children and young adults. It comprises 10 scaffolded lessons, that provide exemplars of how Global Citizenship Education can be taught and learned effectively. The first lesson is centred on exploring the foundational discipline of Global Citizenship Education. Each subsequent lesson focuses on a global theme and on creative ways to critically engage students in their own learning about the world. These global themes include: Our own identity; Belonging; Inter-relationships; Stereotypes; Migration; Seeking asylum; The role of the media. Each lesson follows the same structure: Its particular purpose; Guidance for the teacher; The teacher materials used; Activities and prompts; Final lesson reflections; Additional lesson resources. This Teacher's Handbook is particularly, though not exclusively, suited to the Transition Year (TY) programme in Irish post-primary schools. It may even inspire new short courses at this level. More broadly, it serves as both a conceptual and practical toolkit for how we might think and act differently in our learning responses to a changed and changing world. Education has an inherent power to transform fixed forms of knowledge, skills, attitudes and values, and to positively impact citizenry. Global Citizenship Education holds a special 'anchoring' power in our navigation of 'disruptive' change, including how we cope with climate destruction, civic injustice, protracted wars, rising social inequality, identity prejudice and forced migration. Global Citizenship Education teachers, in particular, play a critical role in meeting these challenges, cultivating hope and re-imagining a better world.