This chapter and the next discuss strategies for choosing between, or combining, different types of study and other general considerations in research design, such as the discrepancies between data collection units and the units of analysis, the use of focused sampling, and the need to cover conflicting interests in research on policy issues. The emphasis in this chapter is on decisions arising within single projects - such as choosing between alternative designs, and multiple replications of the same study. The emphasis in Chapter 11 is on the design of research programmes that combine different types of study into an integrated whole, and related topics - such as triangulation in research design, and the problems of multi-disciplinary research. The dividing line between the two chapters is somewhat arbitrary, because similar issues arise in the design of single projects and research programmes, so they should be read together. Chapter 12 considers some of the practical aspects of research design that can be crucial for translating the initial blueprint into a feasible and successful project.