When to use mixed methods is one of the most challenging issues that health care researchers currently face. The predominance of quantitative methods have not been enough to respond to many relevant questions on health care, that need a multiple approach. Mixed methods have been developed to tackle those problems that pose a complex intervention, or have different and more than two interacting components within the experimental and control interventions, and so many other situations. In this conference issues about when to use mixed methods, how to use them and which approaches of mixed methods are available to be used in health care research.