Research designs can combine qualitative, quantitative, experimental, and data-science methods through careful planning, attention to details and assumptions, and methodological execution. This chapter introduces the book's perspective, arguing that designs that combine methods carefully and with close attention to their details will outperform designs where two or more methods are carried out in parallel and then compared. The chapter also considers a range of practical and philosophical questions related to whether it makes sense to combine methods. Is one method always best, such that it isn't worth trying? Do methods speak fundamentally different languages, such that there is no point? Are methods and problems inextricably linked, such that the question is irrelevant? We argue against each of these views.