Chapter 4 provides an overview of current best practices in dyadic health science design from conception (e.g., who to study and how) to execution (e.g., how to recruit and retain dyads), with a focus on highlighting how intertwined theoretical and methodological considerations should be at each stage of the process in supporting one’s dyadic research questions. We begin the chapter with an overview of the importance – as well as the challenges – of defining the dyad of focus when designing a dyadic health study. From there, we discuss how this definition informs each aspect of research design, from the selection of samples to scales in secondary data approaches and from measurement (e.g., self-reports, observations, and physiological assessments) to recruitment and retention in primary data collection. Throughout this chapter, we underscore the strengths of different design approaches and the need to view these approaches as complementary efforts with the shared goal of advancing the field of dyadic health science.