Sugar-sweetened beverage (SSB) taxes are intended to reduce SSB consumption, and thereby reduce obesity and type 2 diabetes rates. However, SSB taxes vary greatly in terms of design and have been introduced in a variety of different contexts. It is unlikely that each of these taxes work in the same way. My goals are to 1) improve our understanding of how SSB taxes operate, and 2) produce evidence to inform best-practice development. I will apply established social science methods to explore how we can synthesize evaluation evidence without oversimplifying differences in intervention and context. I will focus on SSB taxation, although this approach could be applied to a wide range of population health interventions. I will use a combination of process tracing, with in-depth case studies, and qualitative comparative analysis (QCA). Process tracing is an appropriate method for assessing how and why an intervention makes a difference, and QCA is an appropriate for identifying combinations of factors (“causal recipes”) which lead to intervention success. I will develop key theory around how SSB taxes work and produce evidence which can be used to inform the design of future SSB taxes to maximize potential health impacts. Long term diseases drive poverty, increase healthcare costs and lead to a huge number of early deaths worldwide. Taxing unhealthy products may help prevent such diseases. Taxes on sugary drinks have been introduced in 35+ countries. However, we do not fully understand how these taxes work, or what is the best type of sugary drink tax to maximize health impact. Although these takes are intended to increase prices, they may also work in other ways. I will use existing methods to assess how these taxes work, choosing the most suitable research methods at each stage of my research. I will also evaluate how different tax designs compare, and explore whether these taxes work differently in different richer and poorer countries. My findings should help us to develop better sugary drink taxes that are more likely to improve health. This will contribute importantly to preventing long term conditions worldwide.