"Many systematic reviews are solely concerned with effectiveness or impact. While a review which tells you what works can help you decide what to do, it is of less use in telling you how to do it. Causal chain analysis-based systematic reviews, which analyse the working of a logic model or a theory of change for an intervention, can give useful information on programme design and implementation. Causal chain analysis is not yet common in systematic reviews. This brief lays out what causal chain analysis is, the benefits of using it, and how to do so. The causal chain analysis approach is based on specifying the logic model for an intervention. A logic model provides the basis for the questions to be answered in the systematic review, the types of studies to be reviewed, coding forms, and analysis. The causal chain analysis identifies weak and missing links in the causal chain, and thus which assumptions in the logic model may not hold. Programme designers and implementers can learn from these lessons to achieve better development outcomes." (Box 1: Highlights, page 2)