John Kania and Mark Kramer put forward “Collective Impact” in 2011 as a framework for organizing multi‐sector collaborative efforts to achieve change at scale. The collective impact theory of change posits that by establishing and implementing its five conditions, groups can achieve meaningful systems changes to create long‐term gains in social and environmental conditions. While significant scale uptake has occurred, questions have remained about the degree to which collective impact, as an approach, actually works to achieve change at scale. In 2017, ORS Impact and Spark Policy Institute embarked on an evaluation effort to understand the degree to which the collective impact approach contributed to population‐level change across many sites. We sought to answer this question with as much rigor as possible, without attempting to simplify the complexity of the context, the variability of implementation of collective impact, or the many interim changes needed to see the impact at scale. This chapter shares the essential methods our research team used. We do not seek to share the findings; instead, we hope that others can learn from and use these methods to continue to strengthen the sector's understanding of when, how, and why different collaborative efforts work or do not. In addition to describing the key methods, the authors will reflect on considerations, lessons learned, and recommendations to other evaluators who might seek to answer similar questions or use similar tools and methods.