<p>Scale-up science is complex, but essential in ensuring routine implementation of life-saving interventions at a population-level. Practical constraints in research timelines, availability of resources, and capacities of research teams and wider stakeholders may limit scale-up in real terms. Here we describe our key lessons learned as a cohort of early- and mid-career researchers (EMCRs) with implementation science expertise who had recently completed advanced training in scale-up science. As a group of trainees and implementation science practitioners who are actively engaged in scale-up, we present here some shared learning around “what we wish we knew” before getting started in scale-up, as a means of supporting capacity strengthening of other EMCRs in scale-up science. We present some key learning around: scale-up science terminology; stakeholder engagement in scale-up; and useful theories, models, and frameworks for scale-up. In this commentary, we reflect on some of the key challenges in scaling-up, sharing resources for scale-up that may be especially helpful for the EMCR community, as well as researchers and practitioners engaged in scale-up more broadly.</p>