In this last publication for the 2020-2021 IDS/NIHR Community Engagement and Involvement learning series, we discuss what it means to take a CEI approach that prioritises ‘leaving no one behind’. As with other resources developed in this series, this text builds on a series of conversations between the lead author and a group of Low and Middle Income Country-based experts who bring a depth of experience and critical insights to current debates on what constitutes CEI good practice. The intention of the series as a whole has been to encourage funding applicants to ask themselves hard questions about inclusivity, power and bias as they embark on the initial thinking and design of the CEI component of a given proposal. Here we take on the existing rhetoric of ‘leaving no one behind’ in global health research and how it is sometimes misinterpreted as a demographic tick-box exercise. We ask instead: what is getting left behind in global health research, why is ‘leaving behind’ a phenomena of contemporary development and global health processes, and how can these issues be addressed through a CEI approach, albeit with limitations?