The Reference Book on Comprehensive Sexuality Education (CSE) for secondary school Teachers is in line with Rwanda Education Board’s (REB) commitment to strengthening Teachers’ capacity in CSE as one of the eight cross-cutting issues in the competence-based curriculum under implementation since 2016. The topics and training materials in this reference book are premised on experiential learning methodologies. The wealth of information and techniques they provide are meant to enable secondary school teachers to be more knowledgeable and confident about teaching CSE; specifically, to equip learners with knowledge, skills and attitudes required to make positive and healthy choices for realizing their full potential. The Rwanda Education Board wishes to acknowledge the efforts of a number of organizations and individuals who contributed to the development of this resource material. We would like to acknowledge the technical and financial support from the United Nations Population Fund (UNFPA) and the Joint United Nations Programme on HIV and AIDS (UNAIDS). We appreciate the time and invaluable contributions provided by REB departments, CSE Master Trainers in the development and review of this reference book. Their unwavering support and commitment made Rwanda the first country in East African region to have achieved the 2013 East and Southern Africa ministerial commitment target in 2015 (CSE integration in national curriculum). Special thanks to our teachers and children of Rwanda! You are our hope in helping to nurture an empowered present and future generation.