This paper introduces a research agenda on the implementation of education innovations in primary and secondary schools around the world. We are especially interested in how innovations are implemented at scale and the role of implementation actors in this process. To address the need for a greater understanding of and focus on implementation, we launched the HundrED Implementation Centre for Education Innovation in February 2023. The new Centre will support the spread of education innovation through four pillars: research, practitioner support, practical methodologies, and systems leadership. Under the research pillar of the Centre, HundrED will conduct empirical research that explores innovation implementation at scale in public and private K-12 education in low, middle, and high income countries. We hope this report will invite discussion and debate as well as inspire new collaborators to join us.