Cochrane reviews are systematic reviews of primary research in human health care and health policy and are internationally recognized health care resources for use in a decision-making process . Cochrane works collaboratively with contributors around the world to produce authoritative, relevant, and reliable reviews. Cochrane reviews are commonly used in a guideline development process to determine recommendations for practice. The Cochrane Qualitative and Implementation Methods Group provide methodological advice and guidance to Cochrane as well as leading methodological development to benefit the wider qualitative evidence synthesis community. In this introductory paper 1, we briefly outline the evolution of qualitative and mixed-method synthesis methods, the role of qualitative and mixed-method syntheses in a decision-making process, and the contribution of qualitative and mixed-method syntheses to understand the complexity in complex intervention reviews. We then introduce a series of papers that provide Cochrane guidance on conducting qualitative and mixed-method evidence syntheses for a decision-making context.