This chapter focuses on the use of mixed methods research designs in applied health research. Mixing methods is increasing in popularity as a research approach, but study quality can be poor. In this chapter key issues and resources for those interested in mixed methods research are highlighted, to encourage researchers to focus on important principles and debates to inform study planning. First, the defining features of mixed methods research are explored, and definitions presented. Second, the paradigm challenges of mixed methods research are discussed, with a focus on current epistemological thinking in the area. Third, the issues of design are presented. This includes consideration of the purpose of mixed methods studies, a continuum of study characteristics and a typology of core mixed methods designs. Approaches to mixing data are given particular consideration. Barriers to high quality mixed methods studies are presented. Throughout, contemporary examples from applied health research are used to illustrate key points.